I'm playing a diviner so I forbid only necromancy. But if I were playing almost any other specialist I would most likely forbid divination and enchantment. Enchantment, excepting Heroism and maybe a couple other things, is all will negates, so unless you're specializing in it and taking spell focus and stuff it isn't all that useful. And even after 3.5 changes, divination and necromancy are still the schools with the least number of useful spells.
I think one generic poll is valid if you're trying to figure out which schools are overall the weakest. It seems to me that people will forbid largely the same schools that they don't like no matter which specialist they play.