UPDATE FROM BEASTNODE:
As some of you may know, the Minecraft 1.2.x update came with a huge CraftBukkit update that basically rendered all plugins made for Minecraft 1.1 (CraftBukkit #1988 and below) based servers useless. However, this does not mean they don't work at all. What it does mean is that potential server crashes, lag, rollbacks, and out of disk space errors can result from using them. A very common error we've been seeing is from using an out of date WorldGuard with CraftBukkit 2000+ that causes it to spam the server.log/console until it maxes out the user's disk space. Either install the dev build of WorldGuard (and WorldEdit) or remove it completely to prevent this from happening. Running out of disk space can cause much more problems than just world rollbacks, so it is important that you keep an eye on it. Using old/outdated plugins is not recommended at all and will result in many problems, however, using dev builds of plugins have their own risks also. As always, try to keep everything on your server as up to date as possible as plugins and CraftBukkit are being updated almost on a daily basis that may fix serious bugs.