I only have X.1 on my iBook, which I installed the Word X preview on yesterday since I need it for classes. From I've seen so far it works just fine, smoother than Word 2001 does in 9.2 on my G4, IMO. I'll definately be upgrading to Office v.X when it's released, hopefully the financial hit for an Educational Upgrade won't be too bad...
BTW, the Word X preview says it is good until January 1, 2002. I'm assuming that that is the set date nomatter when you install it.