I am proud to say I know the man, Karl Meltzer, and I was privileged to be able to spend a day with him running the NH section of the trail back in August (Day 10). Here's a picture of us together that day (Karl is the skinny dude).

The website www.whereskarl.com did a fantastic job of covering the event. Here are a few stats I pulled out:
Official Finish: Monday, September 29, 4:20 a.m.
Official Start: Tuesday, August 5, 2008, 7:08 a.m.
Official Finish: Monday, September 29, 2008, 4:20 a.m.
...a total of 54 days 21 hours and 12 minutes.
Unofficially, Karl's is the fourth fastest thru-hike of the Appalachian Trail.
In order, the fastest finishers:
Andrew Thompson: 47 days 13 hours 31 minutes (2005)
Pete Palmer: 48 days 20 hours 11 minutes (1999)
David Horton: 52 days 9 hours (1991)
Karl Meltzer: 54 days 21 hours 12 minutes