EvilSeph released this info about a new Bukkit recommended build yesterday:
New Recommended Build #928.
"This Recommended Build addresses a few API issues and provides Plugin Developers with more events to work with, allowing more awesome plugins to be made. Unfortunately, this new RB WILL break some plugins (mostly plugins that deal with controlling a player's movement - details can be found near the end of this announcement). As always, please be sure to backup your server before updating just in case!"