Petrus is interesting in that he has the measurables the Pats look for. He started 3 games for the Giants last year and the stats don't seem to indicate he was an issue. He started in the last 2 preseason games with the Pats so the coaches got a reasonable look at him (though the 4th preseason game is hardly a valid test). Mallet played with him in 2009 so I would imagine he added another perspective to the decision.
If Petrus does have to take the field, the Colts would be a good team to start out against. Their DL is fairly nonathletic and they tend to bring pressure from the edges, not the interior. Would really rather not see Petrus on the field Thanksgiving against the Jets...so if Mankins and/or Connolly need to heal up, this is the week to do it.