I'm not sure that the Celeron is the worst processor ever. I currently have a Celeron FC/PPGA Socket 370 600 mHz. At least that was what it was clocked to when I got it.
I started with a simple BIOS modification to the highest overclock it could take, 767 mHz. I left it like that for a month, and actually forgot about it.
I just recently changed the jumpers on my DFI CA61 motherboard so I could use the BIOS to clock higher. I tested it at the highest, and it wouldn't POST. I tested it at 900 mHz, and Windows XP locked up for the first time ever on my computer. I'm currently running at 850 mHz, and it hasn't locked up yet.
The main problem I have is that heat locks up the computer, rather than slowing the speed down. I installed a Super Golden Orb, and the problem was fixed, but I won that fan, didn't buy it. I feel for the Celeron folks who have a bad fan.
The Celeron looks just like the Pentium III, except the outside green part doesn't have as much circuitry.