What's the power usage of old PCs like that? I've been using a sheeva plug as my server at home because it only uses something like 5 watts.

It seems like ARM servers are the best choice for home servers. They have adequate processing power and are cheap.

I also have a sheeva plug as my server, but if i did it over I would choose to grab an mac mini. My big jump to the sheeva was the power usage, but then I found out the mini only uses 12W! Along with the 12W you get a x86, with hd, cd drive, wifi, etc on a box that I can easily load linux (upgrading the sheeva's kernel isn't the easiest...) and in a few years when done with it I can easily sell the mini unlike the sheeva.

None of these have over 350W PSU's, and I don't think any of these rigs will draw anywhere close to that power. All I have is anecdotal evidence that my electric bill has increased by maybe $14-$20 a year. Running my stereo for a day probably eats more power than these things take all year. Plus, my livingroom in my apartment stays nice and warm during the midwest winters. I'm pretty happy with spaceheaters with processing power :)

edit: the real issue is that I can't get a cable connection in my neighborhood with higher than .7mbit up, so it's not like I 'm serving loads of content. I use these for running different tasks usually. Two are dedicated DB servers and the other 3 run whatever projects I'm consulting on this/ that week.

I use a VIA x86 system for my server.

18W peak from the wall, no fan (which is one less moving part to fail). Since it replaced an old P4 system (200W from the wall), I shaved $30/month off my electric bill

Home servers? I've always used incredibly out-of-date machines as home servers. There has never really been a market for powerful home servers.

I had a Pentium 166 with 80MB of EDO ram and a 1GB hard disk (bought new in 1996 as a P120 with 16MB of ram) until the end of 2005 as a home server, running Windows 2000.

There is a valid case for "powerful" home servers. Centrally backing up all the PCs in the house and streaming media to computers/TVs/consoles/tablets are two things I do in my house with my server. Granted it's not a brand new system, but it's a Core 2 Quad with 8GB of RAM, 20TB of hard drive space, and a Radeon 5700. Streaming and storing HD video isn't cheap. This centralized server is more cost-effective and convenient than all of my roommates having the media stored locally, though.

You don't need need memory or CPU power for streaming or backups, unless you are doing on the fly transcoding. You do need storage connectivity but even USB2 has a theoretical throughput of 60 megabytes per second while you'll get practical throughput of ~35 megabytes per second on gigabit ethernet.

The only time I saw my ~2005 era system have non-trivial CPU usage was when doing encryption, and even then it would peak at around 25% of CPU.

Encryption and compression are what the CPU and memory are for. The video card is for transcoding to deliver to the target system. It's mainly just a re-used system, but you wouldn't be able to do it with a PII and 64MB of RAM.