Ive been playing as Arcane for a few raids now and I'm loving it, pulling excellent numbers and its also fun to play.
These are really rough numbers though, and whether you're ahead is based on the group you're playing with. If you're still happy with your DPS and topping groups, I suppose there's no good reason that you have to change, but most people are finding better results in other specs.
Well, my guild only has a total of 5 Heroic Bosses killed so far. For most of those Arcane is Ideal when played correctly, so it seems. No one has actually given frost a fair try, I don't think it can compete with the stand still fights, or fights with cleaving. People underestimate Arcane cleaving, it's actually really good. Here are some normal and heroic kills, I did really poor on Feng, mostly because I died to velocity like a scrub, and it really burned me early on. But, with practice and more gear, I think it has the most potential.
http://worldoflogs.com/reports/rt-dojl1kaj8pnjevaa/
To clarify: Right now I'm still performing competitively against people that I feel also perform very well with the gear they have. I'm not opposed to a spec change, but until I've seen more evidence to show that I can at least break even while I learn the spec and then do better once I have it down, I'll stick to what is working.
I also hate to ride the buff/nerf waves too hard. Sometimes you switch and then more nerfs/buffs come and you end up just going back.