The Q1 Ultra I'm testing uses a lowly 800 MHz ultra-low-voltage processor mated to just 1 GB of RAM, a combination that is woefully inadequate for Windows Vista. I've tried to dumb down the UI in various ways to see how performance is impacted, but I can't see a difference between the Classic and Windows Vista Basic UIs from a speed standpoint, so I leave it on the more attractive Vista Basic. Not that it matters: Try to do two or more things at once and the memory dries up immediately and system performance comes to a screeching halt.
Some tasks are simply too demanding for the UMPC regardless of what else you're doing. Playing back a 1500 Kbps H.264 file in QuickTime or iTunes is almost impossible, and even Windows Media Player stumbles through these files with the appropriate codecs installed, providing a miserable overall experience. The supplied Origami Experience won't play these files at all, even with the right codecs installed.
For general note-taking in Word 2007 and simple online tasks (email, Web browsing), the UMPC works just fine, assuming you don't try to do both at once. A RAM bump to at least 2 GB--my recommended minimum for Vista--would likely do wonders, but these machines are never going to be performance champs, not in this generation. If your needs are far less demanding than mine, the UMPC may earn a place in your carry-on. But I don't recommend using it as your only PC regardless. This is more of a PC companion than a true PC, despite the underlying operating system and its capabilities. It doesn't matter if the device is compatible with something if it's not fast enough to run it effectively. This may just be the slowest computer I've ever used.
Paul Thurrott wonderfully described the problems I have seen in this past few days in the Fujitsu U810 that I have been testing. Vista is heavy even in my Samsung Q1 that runs at 100 MHz more. According to Kevin from JKonTheRun, it's more or less OK in his Q1p at 1 GHz. But it's too much for a A110 even when in its new 945 graphic chip Aero looks good.