Can't stand em. I used a hotcorner last year to do a password protected screensaver, because anytime I left my computer unlocked, my roommates thought it would be funny to do various things to it. Coming back from a meal to tub girl as your wallpaper isn't the most pleasant thing out there, so I had to have an easy way to lock the comp. Still hated it because I would always accidentally move my mouse up there when I didn't want to activate it.
Now that I'm on my own, I don't use them and don't have to worry. I just have the Expose buttons mapped to my mouse buttons