Don't feel bad Blake, my fastest CPU is still sitting in its box and it'll continue to sit there for at least another week. Most of the rest of my processors are XP2500s anyway.
My little Appliance PCs
#1:
Mobile XP1700 + low-profile Speeze cooler on a GA7VAXP
Gateway E4200 chassis (it's a full ATX desktop case, but it's extremely compact and nearly silent).
128MB PC2100 DDR
Promise SX4000 RAID controller w/ 128MB PC100 RAM
4x Samsung 160GB drives (480GB RAID5)
1x Samsung 80GB drive (boot)
Intel Pro/1000 NIC
I started initially with the idea of doing something "bare bones" with just a motherboard and this small, empty case, but it mushroomed as I found ways to make it nicer. It's a RedHat 9 machine that has the sole job of accepting backups from some of my other PCs. It wasn't terribly expensive when I built it. The drives, NIC, RAM, chassis and motherboard I already had, and the RAID card was a $50 ebay special. It's probably worth about $700 or so.
Down side: The case gets warm, I had to improvise someplace to put two of the drives (pulled a cage out of an old AT-style case and dremeled in the holes to screw it down) and the stupid #$#%ing Promise BIOS won't detect drives if there isn't a keyboard attached to the stupid thing.
Appliance PC #2: The real deal
P3 1.13GHz on Biostar all-in-one uATX board. 256MB. Lives in Dell Optiplex uATX slim, low profile case. Contains 120GB Samsung drive, not much else.
This thing is like a big, chunky notebook with no display. I'm surprised at how fast it is, but I haven't decided what to do with it yet. I've actually toyed with the idea of putting in my car, say, under a seat, and mounting an LCD on the passenger side dashboard. Wish I knew something about car audio and wiring...