A clever overclocker over in Japan has managed to throttle a Prescott P4 3.8 to a massive 7.1Ghz. Though this is not a strict "world record" (Intel demonstrated 10Ghz ALU's over 6 years ago), it is the first incident where a desktop processor has made it into an OS at that incredible speed. With a FSB of 1520Mhz (380Mhz actual) and PC5400 RAM, this is an overclock worth of a hall of a fame.
Don't expect to get that far, though: This required a very high VCORE of 1.7V and required liquid nitrogen to keep it cool enough to handle it.