My laptop is running a pin-modded Pentium M 1.6 @ 2.13 GHz. Courtesy of a guy who figured out that i915 supported both FSBs, set by a CPU pin. Running since May 05.
My home machine is a Opteron 165 running C&Q but massively overclocked. When I'm not playing games/using 100% CPU, C&Q keeps it at ~1.4 GHz 1.18v. When I run something on it, it clocks to 2.6 GHz 1.45v from its stock 1.8 GHz/1.35v. Totally stable for almost a year now. This machine also has a X800GTO2 that I clock to 520/630, making it faster than a X850XT for the most part. Again, almost a year old.
I've been overclocking since I changed a mobo clock crystal on a 486DX2/66 to make it an 80 MHz. That was around 1994 I believe. Overclocking is a gear-head fascination for me. I love learning about computer hardware and how to tweak it. It's more fun to do this than actually use the hardware, for me.
I'm bored once I get the things working perfectly.
I regularly build old PCs just for fun. I whipped up a Pentium Pro the other month, and I have a Pentium III at home right now for crusty games.
Lots of spare parts and a few cases. I think I have 30 or so video cards, for example, reaching back to some VLB boards. I even have a AMD 5x86 in the closet from about 4 months ago. Wanted to see if I could still do it.
And no, overclocking doesn't reduce lifetime appreciably. I have hardware that I've overclocked for 5 years or so and it still works fine. Of course, this assumes you don't do something stupid like bake your CPU with massive voltage or horrible cooling. Heh.
So, yeah, I overclock. LOL.