This concern that Romney will somehow release his taxes in an October Surprise is just silly...

[D23MIURG23]

21. He has done this before and still won the election.

According to Rachel Maddow a similar line of attack was used by Dems in the 2002 gubernatorial race in Mass. Romney probably doesn't think this is going to be a big enough issue to cost him the presidency, whatever is in those returns. This, of course, may or may not be true.

IMO he is probably using tax loopholes and write-offs that are sketchy at best. I would guess that he would prefer to risk losing the presidency than risk drawing an IRS audit because people (other than his private accountants) have gone over his finances with a fine tooth comb.

Having said that, he could release his returns in late October as a last ditch damage control measure. At that point he might consider it a lower risk proposition given that everyone is going to lose interest in several days anyway. That wouldn't really be a trap though, as you noted. I would also be surprised if that happened given his history of avoiding transparency at all costs. He didn't release his returns in the Mass. governors race, and after his term ended, he erased all of the hard drives his staff had been using.