Before reading, lapping your CPU is basically grinding it down on sandpaper and smoothing out the surface for better heat transfer between the CPU and the heatsink. (CPU's and heatsink's are not perfectly flat when new)
So I've never actually tried it but I have these 2 old CPU's laying around, an old Pentium 4 and an Opteron 265. Lapping the Pentium 4 may be pointless as I don't even have a motherboard for it anymore but I still have everything for the Opteron.
For the Opteron I was planning to wetsand it down to around 1000 grit (working it's way up from 300) because I'll be somewhat using it.
As for the Pentium, I may end up working it all the way up to 1500-2000 grit for a mirror finish and have it sitting around as a decoration or something.
Soooo, kinda curious. Anybody here have any experience with this?