It's not as much jettisoning as it is getting "boned" in trades. I mean whether Gabbard has done something for the Rangers or not, the fact that we gave him up, Murphy, and Beltre (ouch) for Gagne was abominable. I mean it's not that we "jettisoned" Gabbard, as that would imply we DFA'd him or something, but we definitely got boned in that trade.
On the other hand, to your credit many players haven't done well since leaving the Sox. Gabbard included, and in addition to DiNardo and Fossum, don't forget about Pedro, Trot Nixon, Garciaparra, Arroyo, Millar, and possibly Mueller. I'm not sure if Shea Hillenbrand would count either...
So even though the Sox got screwed in the Texas trade (and possibly the 3-way Manny trade) they've done a great job at leaving players at precisely the right time.