I'm guessing you're thinking of door issues, but we just had our first real problem (started using devbuilds of 1.0 Bukkit on 1497, were using 1503 when this happened and are now at 1518). One player tried Lockette:ing (v1.4.4) a chest and the server went into a busy loop. Had to kill the process. He tried again after the 1503->1518 upgrade and then it worked, but it might be completely unrelated to the new devbuild of course. Side note: I just posted a description of how we upgraded an existing beta world to 1.0, if anyone's interested.