Right before the Christmas holidays, my homebuilt 2.4 GHz P4 box went belly-up. Most likely a bad motherboard, but I was just tired of messing with it.
So I scavenged almost everything I could out of it and started hunting around for the current price/performance breakpoint in "Intel-based" PCs. Turns out that title belongs to the very inexpensive 64-bit AMD CPUs like the Sempron. Ended up with an Asus Vintage AE-1 "barebones" system from Directron - one of my favorite PC parts suppliers.
One of the big advantages of doing business with Directron is that they'll assemble & test any PC components you purchase for a very reasonable fee. So I had them drop in an AMD Sempron 3400 and 1GB DDR400 RAM in to the AE-1, test it, and ship it to me. I then added my DVD burner and AGP video card myself and badda-boom, new computer. Both WinXP and Ubuntu Linux installed easily (had a minor work-around with Ubuntu & the SiS190 ethernet chipset on the AE-1 motherboard, but nothing serious), and for just over $300 I have a small, speedy and quiet new system.