If Greg McElroy takes the field in a 2011 regular season game, either something really good has happened to the Jets or something really bad has happened. The plausible scenarios seem limited to garbage time in a Jets blowout win, garbage time in a Jets blowout loss, and injuries decimating the position and forcing McElroy into the lineup. (And Brian Schottenheimer installing a formation with three quarterbacks on the field...which fits the "really bad" criteria).
Considering the learning curve, it is best to keep a rookie quarterback on the sideline whenever possible. Situations like Mark Sanchez's rookie year in 2009 happen where a team is so thin that a rookie has to play. However, the Jets will want to keep McElroy off the field. He will not likely be second on the depth chart to start the year. The 2011 season will probably be about learning the playbook, adjusting to an NFL lifestyle, and picking up on the speed and complexities of pro defenses in practice and film study.
McElroy is not guaranteed a spot on the roster, though. It is entirely plausible that he will be cut if he bombs. Kellen Clemens might not be back, but Kevin O'Connell and Erik Ainge are under contract. The Jets stuck with Ainge through drug rehab. They gave O'Connell a contract while injured. This was no charity act. They want to see what they can get. If things are even close to even, McElroy will probably get the nod for the third quarterback spot. The team took him evidently because the others have not impressed the team enough to prevent the pick. A rookie playing at a certain level also has higher upside than guys with a few years of experience playing at a certain level.
If all goes well, McElroy is more Matt Flynn than Ken Dorsey and can become Mark Sanchez's primary backup in 2012. A few years later, perhaps the Jets can flip him for a bounty better than the seventh round pick invested in him this year.