you shouldn't shy away from a guy just because "busts" you have drafted from the same school in the past. i still don't consider chad jackson a bust, i'd give him a full year with a team to see.
anyway, i know there are needs on defense, but there are many things about harvin that make me think belichick would love to add him, especially if the pats pick up another first rounder for cassel. belichick loves versatility and deception. those are two key things harvin offers. he can line up out wide opposite moss, in the slot, or in the backfield. he can be used in the run game, on deep/intermediate routes, on bubble screens, and on short check-down routes.
you have to figure we have moss for this year and next year and that is it. during and after that 3rd year he'll definitely be slowing down and even if he is brought back he won't be the elite WR he was. percy will almost certainly never develop into a #1 wr like moss, but he is an explosive playmaker to replace moss when the time comes. even if you say you would rather draft or sign a different WR when moss' time is up, that's fine too. then percy can be used as the successor to kevin faulk. we all know how important faulk has been to this team, and with harvin's great speed and ability to make people miss you'd have to think he'd be an ideal replacement. he could also be used on KR and PR to spare hobbs and welker from those duties.
i know there are some questions about his durability, and that should be taken into consideration. but this guy was a dominant playmaker in the best conference in college football. i remember reading/hearing how he's actually got better speed and better lateral quickness/agility than reggie bush.
there's no doubt he'd add explosiveness to the pats offense and a great receiving option, but i think belichick would LOVE the versatile and deceptive ways he could use harvin against opponents. harvin could have a huge impact on 2 out of the 3 phases of the game (offense and special teams) and i think belichick would love this as well.