I had an Athlon XP box in early 2003 that I enjoyed using. With a Radeon 9000 and 256mb PC133 and a 40gb hard drive, it wasn't high end but it ran pretty nice and I enjoyed use of it for a little while. Unfortunately, with a dated Via chipset that had been around since the Thunderbird days, PC133 and a video card that was dated when I got it, by 2005 the computer was pretty washed up. I would have kept using it a while longer but, unfortunately, the CPU burnt out when the fan quit working and when I replaced it, the motherboard was acting funny; computer was just never the same. It's interrim replacement was a 500mhz Coppermine box (actually a 667mhz chip underclocked) mated to a motherboard with 440bx. At the time, I never noticed a substantial performance decrease in actual use though there was a significant difference in benchmarks. I'm sure today, the Athlon would feel a lot faster but with software back then, that wasn't so.
I want to build a socket 478 box for myself; I have an empty ATX case and plenty of old chips (a few Athlon XPs, a Duron) but every motherboard I've come across this year turned out to be rubbish. Of the sseveral socket A boards I've encountered in the past two years, the only really decent ones were the DFI nForce 2 mobo I used to upgrade my mom's computer and an MSI board with a SIS chipset I wound up giving to a friend.