In the 3rd round, the Patriots took WR Brandon Tate from North Carolina. This guy was a potential 1st rounder until he tore his MCL 5 games into his senior season. He also tested positive for marijuana at the combine, which is more of an indictment of his intelligence (every player at the combine gets tested and everyone knows that) than his character.
The Patriots don't need a receiver, which is why it's fine to wait for the 3rd round and take a shot on a guy who could wind up as a good NFL receiver. If he doesn't, no big loss.
The Pats obviously have Moss and Welker, along with Joey Galloway, Greg Lewis, and Matthew Slater. Tate could sneak in as a #4 or #5 receiver on the depth chart, and as Moss and Welker get old, Tate could be a very good receiver for the Pats' for years.
Or he could decide to get high even though the NFL substance abuse people will be watching him like a hawk, and literally piss it all away.
The Patriots also traded two of their 3rd round picks for a 7th round pick and a pair of 2nd rounders in the 2010 draft.