There are two ways to look at this topic. What level of gems should I use and what stats should I look for in my gems? Both questions are fairly easy to answer but I am surprised at how many times is see people make the incorrect choices. Here are my thoughts.
I assume that most of you already know this but I have seen quite a few posts that say "rate my moonkin" that fail some of these basic rules.
White Gems - Most people don't even know they exist but you can by white level gems from a vendor. My advice is to not do it. Yes, they are cheap and easy, but green gems are just as cheap and easy. The only time I would consider equipping a white gem was if I was about to do an instance with a new piece of gear and the AH didn't have the gem I needed. Even then I would replace it as soon as I could.
Green Gems - These are great for Green or Blue items that you probably will replace fairly soon. They are also very good for off spec and alt gear. No point in spending 50g for gem that you won't use often.
Blue Gems - Pretty much a must for Epic level gear. If you want to raid more than casually then having these gems are expected at a minimum.
Purple Gems - There are now several sources of epic gems. You can get them from T6 raiding, Badges of Justice, Instances, and PvP. High end raiding guilds are starting to expect you to be gemed with epic gems. So If your hope is to see all the game content before the expansion, then you will need these.
This is where most people need help. I will look at it from the stand point of each socket type and then talk about some of the pitfalls you should avoid. I will also use blue level gems as my examples but you can use either the green or purple level gems if you like.
Meta - [Chaotic Skyfire Diamond] is your best option. This is the one and only time I will say to stack crit over spell damage. I do that because the extra 3% crit damage is awesome. In actuality it improves your Crit damage by 4.5% due to blizzards crazy math. For a kara/gruul's level raiding moonkin it is equivalent to 20 - 30 spell damage. For T5 and T6 moonkin it is more like 50 spell damage and can go much higher. The runner up is the [Swift Starfire Diamond]. I only mention this because it is cheap and easy. Not a bad choice for socketing an alt or off spec.
Note: Meta gems have other requirements to activate them. The [Chaotic Skyfire Diamond] requires two blue gems. This means you have to have two blue gem types socketed in other gear. However they don't have to be pure blue gems. You can meet the requirement using Purple or Green gems also.
Red - [Runed Living Ruby] is the best choice most of the time. Spell damage drives your DPS and this gem gives the most of it. [Veiled Noble Topaz] is another option if your below the hit cap. If you have 1400 buffed spell damage then [Reckless Noble Topaz] could also make sense if your are stacking haste.
Yellow - Spell Hit, Spell Crit, and Spell Haste are more expensive stats then Spell Damage. Gems are the perfect proof of this. The [Runed Living Ruby] has 9 Spell Damage where as the yellow gems for hit, crit, and haste only have 8 points in their stat. That is why I prefer to socket yellow sockets with orange gems. You should focus on the [Veiled Noble Topaz] until you are hit capped from gear. However, the [Reckless Noble Topaz], [Great Dawnstone], [Quick Dawnstone], and [Potent Nobel Topaz] are also decent options if they fit your situation. Don't stack Haste until you have at least 1400 Spell Damage buffed. Crit should only be stacked if you are hit capped.
Blue - [Glowing Nightseye] is the best choice. Spirit, Mp5, and Spell Pen are the only spell related stats available in blue, and all of these stats are either expensive or useless. Thus, the Glowing gems are always the best option.
I find that you should equip for the socket bonus 90% of the time as a Moonkin. This is because a majority of socket bonuses are additional Spell Damage or Spell Hit. I think socket bonuses of Stam or Crit are a matter of personal preference and how far out of your way you have to go to get the socket bonus. Any other socket bonus you should ignore for the most part. In these situations I would equip Runed gems.
Intelligence - Gemming for Int is a common error for a lot of new moonkin. They see all of the damage, crit, and mana we gain from it and assume that it is our best stat. Well, it isn't. It is a very good stat but you will get more DPS out of straight spell damage then you will out of Int.
Mp5 - Moonkin have a history of having mana problems and therefore some moonkin are tempted to gem for a little extra mana. The problem with Mp5 is that it is so expensive. You can get 5 spell damage and 6 stam at the expense of just 3 Mp5. It just doesn't have enough bang for the buck.
Epic Gems from Instances - There are some very good gems that drop out of instances. [Glowing Tanzanite] drops in heroic BM. [Shining Fire Opal] drops in heroic Mech. However, these are the only two gems you should consider equipping out of instances. Don't feel like you have to equip the 5 hit/2 mp5 gem just because it dropped. Equip what gives you the best performance.
There have been some changes made to the Alpha leak Wiki. If you would like to look at the Wiki your self you can find it here. Just remember, that none of this is final and it may be fake. Browse at your own risk.
Eclipse - now lasts 30 sec (up from 12) and has a 2 min cooldown. - I didn't like this talent in the first place and this change doesn't make me like it anymore. My main question is what is there intent with this talent? Is it for PvP or do they expect it to be used in raids?
Owlkin Frenzy - 25% spell haste ditched, now gives balance spell pushback immunity on proc. - I'm not sure if this is a nerf or a buff. Probably a bit of both. The pushback resistance could save you as much casting time as the haste especially if you are trying to get a Starfire off. Anyway, this is still a very PvP focused talent and you all know I am not a PvP expert.
Imp Moonkin Form - 100% spell haste changed to 20%. - I said in my original comments that this was an overpowered talent and wouldn't make it to release. Well, as predicted it has been nerfed to a much more reasonable level of 20%. It would make my Starfires a 2.5 second cast. I think this is a good level, but I wouldn't be surprised if it was lowered a little more.
Soothe Animal - Now affects dragonkin. - Has anyone ever used this spell?
Celestial Focus, Vengeance, Focused Starlight, Moonglow - Now also affect Starfall. - Not a surprise.
Entangling Roots - Now ticks every second. - Just means a little more damage if it breaks early and makes it a little more affective on casters by causing more push back.
Lunar Guidance - Changed to 4/8/12% (down from 8/16/24%). - A HUGE nerf that will cause a lot of moaning and groaning in the Moonkin community. If it was implemented right now I would lose about 70 spell damage raid buffed. I don't like it but we will see what happens. Phaelia over at Resto4Life thinks this change is primarily focused at discouraging the Dreamstate build. If this is the case there has to be a better way to do it. Here is her evaluation of the new changes.
Starfall - Extra damage radius changed to 5 yards (down from 10). - A nerf but I still don't understand enough about how this spell works to voice much of an opinion on it.
Nature's Fury - No longer converts bonus healing into damage. - Not huge. This would make this talent useless in PvP, but leaves it still vary viable for Raiding.
Graylo - I didn't play a whole lot over the weekend. I have a lot of family stuff coming up so my playtime will be limited. I did the first four bosses of ZA on Saturday, I wasn't able to get on early enough to try and finish it up on Sunday. Nothing special here I just got some more badges.
Graypal - He is really on the back burner now. I didn't do Kara with him because I was busy this weekend and I don't really have any other reason to play him right now. I did get a couple of heroic runs on him during the week and I am very close to revered with Sha'tar so that I can get the head enchant.
Grayfel - As is usually the case I had hoped to do more with him then I did. He is now two thirds of the way through level 52. I had hoped to get him to 53 but it didn't happen. I can really see the light at the end of the outland tunnel. I know that I am 8 levels away but i feel very close. His professions are doing ok. I think his mining is up to 269 and should easily be 300 by the time I hit outland. Jewelcrafting isn't going as well. I think I am up to 218 or so. I need a ton of [Aquamarine] to level it up and they were selling for 5 gold each over the weekend. I think I have some time to get it up but I hope to be 300 by the time I reach outland.