While I'm not going all-out and getting 10 games that will net me an extra $25 credit or anything, I did pick up 2 copies of one game that all by themselves will get me $25 more than what I paid by trading them to BB. Since it seems the BB trade-in is only online like Amazon, hard to say how successful it is yet.
As to AC2, has anyone actually been able to get the 29.99 price using that trade-in deal? Last I heard it didn't qualify due to being on sale already.
AC2 would require you getting a very lenient employee or manager who would allow an on the spot return on something else that goes for $30 new now like Little Big Planet GOTY or Killzone 2.
However, that would definitely look a little fishy if the employee did an on the spot return of a game you just bought. So unless you have 2 Gamestops within close distance of each other or really cool employees at one to allow the above, you might be SOL.