I built my girlfriend a shuttle system about 4 months ago that I plan to eventually steal back and turn into a PVR box with my ATI TV wonder when we move. Her system wasn't the most cutting edge but it's actually nice to work on.

Nforce2 MB, Integrated graphics (she doesn't play games) and audio
AthlonXP Barton core, 2500+ 333FSB
512M of Cruicial DDR400 (DDR333 was $2 less)
WD 80G 7200rpm 8mb HD
Liteon CDRW (from old machine)
Linksys 11b PCI card (from old machine)

I think the grand total was around $500 for all the parts. I could have built it a little cheaper not using the shuttle but a regular ATX box but these SFF systems are actually pretty cool. Her's has one of the later SilentX power supplies (I think they all do now) and when the machines running, you can't even tell it's one except for the lights. I'm probably going to yank the Wifi card (she gets free internet from her neighbors) and put my TV tuner card and maybe a decent $150ish AGP card in it someday and probably stuff a big HD in it to record shows. Anyway, long story short, I like shuttle but it's a little more expensvie.