If you're the GM you can start bossing people around a bit.
Or get a mean officer to do it for you.
Also, definitely log your raids for WoL so you can see who is underperforming the most, and if you can determine why.
And as a general thing, have you tried telling people that they're not cutting it/demanding from them that they improve?
What I also recommend is having people state in /raid or over vent why they died and don't accept "I don't know".
Of course, if you wipe you only have to hear that from the people who died before things got out of hand.
Checking if what they say is correct in Recount is also a must. (Not because I think people lie about it that much, but because people are just wrong very often)
In my experience, if people realize why they died and are forced to admit that they've made a mistake they don't make that mistake again anytime soon.
Edit: I forgot to add, this also stops other people from making the mistake as they just heard what went wrong and why.
It is your task then to make sure it's not seen as ridiculing someone but as a learning process and needed to improve and kill bosses etc.
Not the easiest task, one that will get you to say "It's not to ridicule you, it's so we can all learn from it" and more of those things like a broken tape.
Edited, Jul 20th 2010 9:44pm by Aethien