If it really will be released after Longhorn, this could take a while... Longhorn, while they say it'll be out next year, could easily not be. Microsoft is notorious on their release dates. Even if it is released, chances are they'll be cutting most of the features, and the ones they do have done, will probably be backported to XP...
Sure, the device itself looks cool, but...
1) When will someone hack it to run Linux?
2) That's not exactly a small device... It's pretty large...