Some dudes I know are going for 8GHz on a p5b... It's crazy, they have done all sorts of vmods to help push towards their 8GHz goal. At the very least, the extreme cooling setup is worth a quick look. Here's the link: http://digg.com/hardware/8_Ghz_overclocking_project
Wow, awesome. Not sure they'll get there, but that's all down to the chip's and how skilled they are with the LN2. Some of the facts on P2 about electron migration and absolute 0 are a bit iffy, but close enough.
Pretty cool, but hasn't the 8Ghz barrier been broken by a P4 631 and a P5B-Deluxe before? Either way, good luck to them on breaking 8Ghz!