I've got a GX110 and a GX1p hanging out at home, and I really like them -- the GX110 (PIII/933, 512mb/20+20, cdrw) out performed my G4 PowerBook on SETI, and the form factor is pretty great.

My next surplus PC will probably be one of the more rounded midnight gray systems, like the GX150 or one of the 2x0 series.