I used to do MCO-CLE and never had any trouble. I work for CommutAir which flies as CAL Connection. We could sit in the cockpit but were lower priority than Mainline or XJT. In the year and a half I did it (stopped commuting in Sept '04), I only ran into other jumpseaters two times. One was a mainline guy going to CLE. Fortunately it was a 735 which had two jumpseats. The other time was an XJT guy going on vacation from CLE to MCO. He got the cockpit jumpseat on the 9:05am flight, and I was able to catch the 9:50am flight. I stressed about it a lot, but never missed a trip. Obviously being mainline, it would be a little bit easier.
I tried TPA a few times but gave up on it. CAL has a large reservation center in the area which leads to a ton of last minute non-revvers, and there are a few more guys who did the TPA-CLE commute than did from MCO.
I never tried EWR or IAH, but the gate agents in both TPA and MCO said they get a ton of mainline guys on those flight.
If I were ever to be so lucky to get on with CAL, I wouldn't hesitate to do MCO-CLE, but others I wouldn't be eager to do.