I used to. But I liked to have my pc on 24/7 so I don't have to wait for it to boot if I want something done, plus I had a shared printer.
As I have aged, I have had less and less time for gaming, and most other tasks just need to be 'fast enough'. And then components needed to be replaced.
My last two builds are both 45W procs and still on 24/7. One of them is now a NAS box and has actually been undervolted, but not underclocked.
I'm sure I am in a pretty rare minority here.
Right now, neither. I have a i7 920 and can't be bothered to adjust all the memory timings etc.. When I get an unlocked Ivy Bridge I'll most likely overclock it though.
I haven't OC'd my 5850 either since I just haven't seen the need.