I can't stand XBMC's interface. It forces you to organize things the way it thinks you should, which really pisses me off when it comes to movie and TV series. If it had the level of customization that iTunes has, where you can tell it exactly how you want it sorted, that would be great - but no, you have to use the "scene" sorting with XBMC. So I'll never use it until that's fixed.

Besides, HTPCs aren't very portable, which is a big part of why I like both the Seagate and WDTV. You just unplug it, grab the cables, and take it and your hard drive with you to your buddy's place, no hassles whatsoever.