Well, I purchased the Shuttle XPC SB51G last week and I'm going to guinea-pig it on the sister in-law. If all goes well with her (she's really not a hardcore end-user) I'll consider it for my own.
My only real drawback to this model is the Socket 478 board (not an intel fan), and a paltry 200W power supply. Otherwise it's seemed rock-solid so far. The fan is not too loud, and they are combining the PS fan with the cooler for an oil-cooled cpu sink. (I dont not certain how effective that would be for a higher-end rig.

This board has 333/400fsb on the 478 Socket, I installed a p4 2.4
2 Dimm slots to which I installed 1 512 333mhz DDR stick
Onboard intel extreme gpu (Also has an AGP slot)
AC '97 onboard audio with 5.1 support (has spdif on front/back!)
Room for 1 CD-R 5.25 bay, and 2 HD 3.5 bays (ata100)
They didn't skimp on the ports. standard ps/2 kb & mouse, 2 serial, 2 1394, 2 USB, rj-45, and standard audio in/out on both the front and back

It's not really as beefy as I would want for myself, but the girl is a web surfer/music burner. She really doesn't need bleeding-edge performance.

But probably the biggest diescision in my purchasing this box (and I laugh at myself for this) was cosmetic.

Yes folks, I intend to build a Hello Kitty mod!
A nice set of stickers will adarn the case. I've reconnoitered a hello kitty pink keyboard and mouse. I also managed to snag an old 15" lcd monitor to which I will apply disgustingly cute pink paint.

Laugh and be amazed...