I too was puzzled with this question, what spec to go after 3.1! After trying out what was on the forums etc and almost every variation of fire imaginable, i still saw a drop of about 2k dps from pre patch.
This is why i went back to arcane. They are so close and the only reason fire is slightly better is for the scorch debuff which is pretty crap anyway.IF you are like me, not hit capped, go arcane, this means you will deal so much more damage! You also ahve so much more SP etc which gets you into raids easier!
Basically, im sticking with the old arcane spec with a few variations for mana regen Talent Calculator - World of Warcraft .
Iv found much more dps with this than any other spec (so long as you can keep your mana up, which is very tricky at times). Also after testing with RAWR, i found that using arcane missiles after 3x ABlast even when it DOESNT proc gives more damage output than Arcane barrage! this means that you should only really use barrage when you are on the move! From more testing, i found that when Blood Lust is used, simply spam arcane blast (be very weary of your mana here!!!).
The only downside to arcane is the mana consumption! Arcane drinks mana faster ever! This means that you must try and use every single mana regen capability within your power, i usually wait until i get to about 75-80% mana until i use my mana gem (when i blast all my CDS to include the managem set bonus buff) and after all my cds are done i shud be down to about 40-50%. This is ususally when i use my evo, or i save it if higher than 40%. You should always have mana pots for emergencies! Also make sure you have the glyph of mage armor! This combined with the talent makes your aman shield regen 100% while in combat! This is a must have!
Thats pretty much it! Sorry for the huge wall of text! :P