I don't think fire mage is weak. Good mobility, reasonable damage, good CC. In pugs they certainly do fine.
Ele is weak for sure. Purge is very strong and it's the reason blizzard is afraid to give shaman decent numbers or survivability. I'm currently playing one. Pretty fun.
Affic lock is also fun. You can pretty easily get top damage (at least that's how it was at 24, I haven't seen too many lock twinks lately), but your impact on the game is fairly low.
I'm not a rogue expert, but I think they are in a wierd place right now. They used to be pretty faceroll, but now it's a case of bad ones do nothing for your team and good ones often carry hard. I'm not saying they are bad, but I think the skillcap is pretty high.