I still think it could be done. Members with >x number of posts could be eligible for troll voting and members with over >y number of posts could be excluded from being voted a troll, one of the pleasures of being a good forum member
It would certainly make people think twice about dumping in forums if they knew they could be visually labeled as a troll. Think of it as a kind of self regulation for new members.
Posts that were voted as being troll posts could be reviewed at a later date and the mods could then decide whether it was a fair vote or not, people who troll vote to often could simply have the priviledge removed. If it was done correctly it could save the mods time and effort in castigating the monkeys who make such a mess in the forums.
It's just that it really annoys me that we don't really have any way of marking these people.