I have the EX490 that I got a few months ago. Since the main objective was to back up multiple computers in my house (and some that I use for work), the HP certainly is a bit overkill in the feature department, but I figured that I'd use the other features at some point and at the time, I just wanted to get something that would work without much hassle (no build/config time). I did order an additional WD 1TB Caviar Green for "balancing" the storage - as I'm paranoid about data loss.
I agree on the looks of the machine - you can't get much better. It's small, so can be as inobtrusive as you want, but it also looks good, so you can put it out in public.
Functionality wise, I really haven't stretched its capabilities too much since, as I mentioned earlier, it is mainly for backups. However, I have played around a bit with media storage and streaming and so far everything has been solid. I have run into some issues with some machines not authenticating correctly with the home server, but the issues are hit and miss.