I like them, it is a fair way to punish people for being immature, with the warnings not there, we would probably see a bunch of people who think the mods aren't going to punish them, then they go ape shit on the forums.
We should add another warning level before any bans take place, I think it would be more intimidating to have an admin pm about the warning then a mod, but whatever, that one would be "Last chance before a vacation, dont fuck with me!" kind of warning, it would definantly justify a perm ban, because after 4 warnings you are just asking for trouble.