Certainly you have to say that a part of the Orioles' success this year can be attributed to some of the players that Dan Duquette brought in in the off-season. What's a little more interesting, is that as of yet, there are no real regrets over players the O's lost from 2011.
Jeremy Guthrie. Sent to the Rockies in the Jason Hammel trade, which many people panned at the time (incorrectly, in my opinion). Not only has Hammel been quite good with the O's, but Guthrie has posted a 4.80 ERA for Colorado and (after being traded for Jonathan Sanchez and his 7.76 ERA) Kansas City. His vaunted base-hit suppression skills were no match for Coors Field (.318), though they did return to normal in the AL (.273 BABIP). Also seeing a big split was his home run rate; 2.1 HR/9 for the Rockies, and 0.8 HR/9 for the Royals. A Jeremy Guthrie doing what he's done for KC (3.00 ERA, 3.61 FIP, 1.6 fWAR) would have been a nice addition to the Orioles' rotation, but there's no guarantee of that - taken altogether, his 1 fWAR would rank just 5th amongst O's starters (and that's despite having more innings than anyone on the team but Chen).
Luke Scott. He hasn't done much more with the Rays (.227/.279/.438, 0.2 fWAR) than he did with the Orioles last year (.220/.301/.402, -0.1 fWAR). Pretty much every conceivable alternative the O's used this season (Betemit, Reynolds, Davis, Thome, Nick Johnson!) has out-hit him.
Derrek Lee and Vlad Guerrero are out of the Majors (Vladdy played a few games in the minors for the Blue Jays).
Josh Bell (traded to Arizona in May) could theoretically have blocked a Manny Machado call-up when the O's needed a third-baseman, but Machado has outplayed him (Bell's hit .173/.232/.269 in the Majors with -0.5 fWAR, though he has done a nice job in Triple-A as a 25 year-old; .311/.372/.509). Bell still has a chance to turn into something (only 282 career PA in the big leagues), but it's possible that having him in the organization in 2012 could have ended up costing the Orioles a win or so.
Felix Pie is hitting well in the minors for the Braves (.285/.338/.459), but Nate McLouth hasn't been much "worse" than that in Baltimore (.267/.339/.413) and I'm pretty sure the O's are fine with the guy they have of those two at the moment.
Cesar Izturis has been a replacement level player this year (and pretty much the last couple years), though he can still field a little bit and has been better than Omar Quintanilla (-0.4 fWAR for the Orioles) or Robert Andino (-0.3 fWAR). Having an actual second-baseman this season would have been pretty nice, though I doubt there are any fans pining for Cesar in particular.
Craig Tatum has hit .179/.258/.286 in Triple-A for the Yankees, while Taylor Teagarden has approximately 57 game winning hits.
Brandon Snyder took it to the Orioles when the Rangers came to town early this season, but he's been a slightly below average hitter this year (.277/.309/.446, good for a 98 wRC+) and that's with a .417 BABIP. Similarly in the minors, minus 55 points of BABIP (73 wRC+).
I miss Koji Uehara out in the pen, and he's done a nice job in relief for the Rangers; 2.15 ERA, 10.3 K/BB ratio (still has the best mark of all-time at 7.55 K/BB, min. 100 IP). I'd gladly swap out Koji for Kevin Gregg, but it's hard to complain about the O's missing a quality bullpen arm given how things have gone in that area for the team this season.
Similarly, Alfredo Simon is doing well in Cincinatti; 2.48 ERA, 2.95 FIP, and 0.8 fWAR in 54 relief innings. I think Simon is better than Luis Ayala, but - again - don't want to mess with that magical bullpen.
As far as non-Major Leagues players, the O's shipped off Jarret Martin (4.40 ERA, 9 K/9 but 5.6 BB/9 in A-Ball) and Tyler Hanson (.284/.374/.468 in Triple-A) for Dana Eveland (4.73 ERA, 0 fWAR) which was not a well received trade at the time (by me, at least) and has turned out about as expected (not disastrously, but certainly not well).
They also sent Randy Henry (3.38 ERA, 2.1 K/9 in High-A) and Greg Miclat (.275/.350/.394 in Triple-A) to the Rangers for Taylor Teagarden, which is probably not very good in the abstract but fine for the O's when you consider the big hits Teagarden has had.
So overall, the Orioles didn't lose a great deal of talent from the organization since 2011. Maybe they'd take a do-over on a move here or there, but it's hard to think that they're missing a piece that could have actually done much to improve the 2012 club.