I read one of Notch's tweets (retweeted to my phone, rather) about pressure plates + pistons = unrecoverable SMP maps. Lmao
http://twitter.com/#!/notch/status/86499931354959872 Looks like we will have to wait a while, he's already slacking off and waiting until tomorrow...xD And also pistons still cause crashes even after he "Fixed" that, it happens when they mess with redstone or something like that, just even more time to wait.