In 2008, Anthony Collins (#112) was picked over Carl Nicks (#164). Collins was ranked #78 overall so it was a very good value and has turned out to be a decent pick (Nicks has been better but wasn't really a scheme fit).
In 2009, the Bengals selected Jonathan Luigs at #106. Cook spent part of the previous year on IR (dislocated toe) and we had seen enough of Eric Ghiaciuc. Luigs was ranked #132 overall so it wasn't much of a reach and certainly understandable given the need. No centers drafted after Luigs has panned out in the NFL. Luigs would washout due to injury.
In 2010, Otis Hudson (#152) was selected over Marshall Newhouse (#169) among others. Newhouse was rated #175 overall whereas Hudson was way down the list at #460. Newhouse has started 29 of a possible 32 games plus 2 of 3 post-season contests. He's allowed 10+ sacks per year though, which either reflects his poor play or the fact that Green Bay is always throwing the ball. He plays LT for the Packers but would have projected inside for the Bengals. You can argue that Hudson was never healthy but it was still a reach in the draft and the equivalent player ranked closer to pick has proven to be a solid player.
In 2011, Clint Boling was picked at #101 but was ranked #74 overall. A good value pick and clearly one that has been validated by his play.
This year they picked Tanner Hawkinson at #156 despite being ranked #327. The team admitted he won't see much action until he improves his strength, so why use a 5th round pick? If they wanted tackle depth, Jordan Mills, Vinston Painter, and even Reid Fragel were still on the board. If they wanted interior depth, Jeff Baca and David Quessenberry would have been good value. Time will tell on this pick. Hopefully Hawkinson turns out better than past reaches. When the Bengals / Paul Alexander select lineman as value picks it seems everything works out; when they don't...well, it's pretty obvious.