For another forum I made a stats-based comparison of Cassel and Thigpen, which I thougt you might enjoy here. Basically the conclusion is that based on last years stats, Cassel really isn't any improvement, but probably not worse either. Obviously with having taken over his franchise tag, the new contract makes sense, but whether it was a good idea to get him in the first place remains to be seen.
Cassel: 3693 yards, 21 TD's, 11 ints, completion % 63.4
Thigpen: 2603 yards, 18 TD's, 12 ints,completion % 54.8
So far Cassel looks a lot better. Now let's disect those stats.
First up yardage: Matt Cassel was league leader in YAC percentage with 57. That is more than half his yards were after the catch. Thigpen had a YAC percentage of only 42. If we take away YAC, Cassel is down to 1577, while Thigpen has 1507. If we further take away sack yardage, Cassel is at 1358 and Thigpen 1345.
Touchdowns: Nothing to say there. Cassel had more.
Interceptions: Thigpen had more interceptions in fewer games. However Cassel got sacked a lot more than Thigpen and lost 5 fumbles, whereas Thigpen only lost 2. So in total turnovers Cassel actually has 2 more.
Completion percentage: Cassel's best stat compared to Thigpen. However a slight modification is still in place here. Many incompletions occur because the ball is thrown away to avoid a sack, and so if we should look at completion/(pass+sack), giving Cassel a percentage of 58.0 and Thigpen 51.6.
Now let's finally look at the adjusted stats per passing down:
Cassel: 2.4 yards, 0.58 completion, 0.037 TD, 0.030 turnover
Thigpen: 3.0 yards, 0.516 completion, 0.040 TD, 0.034 turnover
Basically it's quite even. Thigpen takes more chances, but that is probably mostly because of the system.