Most importantly of all (apart from the obvious 'does it play music & videos' functionality), it doesn't require me to use that dreadfully clunky and unresponsive piece of software called iTunes. I'm running Vista 64-bit, on a decent PC - plenty of RAM, and a fast dual AMD CPU, so there really is no excuse for iTunes to run slowly when nothing else does.
It's taken me a little time to find the sweet spot in video format to minimize audio glitching - but it was just the realisation that you have to run the supplied video converter software at the highest quality (& slowest conversion speed, of course) to get the best results.
I've not returned to work after the holidays yet, so I've yet to see how the device functions in that part of my life, so expect more on this another time.
One odd thing though, and it's really a criticism of Google, or the 'net as a whole. When I google for information about the X-Fi, I get the best part of 10 pages of people either selling it, or 'professional' reviews. On those pages where there are comments from real people, there's so much Apple/anti-Apple fan-boi noise that sensible, vaguely objective experiences are hard to find. Where have all the bloggers and sane people gone?