It's more like 50% not 90%. Anyway about half the guild I'm in tries to do heroics the other half kinda gave up on them.
The problem is that heroics have to be done raid style if you want to actually finish them. If you try lfg pugs, 4 out of 5 fail before the first boss.
Basically it's 5 man raiding. You need the right team mix, everyone to be ready at the right time and so on. This is not good for me, not for heroic 5 man dungeons. Cata is now hardcore and you need 4-5hours/day if you want to do something.