I was at the dealer for an oil change (full synth) & tire rotation this morning (oddly, the dealer is cheaper for that than most garages in town- wtf?) and I mentioned my repeated minor issues with the gas cap. When the Service Advisor returned, I expected to have a completed oil change & a new gas cap. Nope. He said the filler neck itself had a small abnormality in its threads that was likely binding up the cap on removal, so they needed an extra hour or two to replace the filler neck.
They also offered to put me in a loaner if I had errands to run, etc., so kudos to Ferman Mazda of Brandon (Tampa) for that. I had nowhere to go & plenty of video podcasts stored on my Zune, so I waited.
Of course, I won't be certain that the problem is fixed until I have filled up at least 8-10 times, but for those having cap removal trouble, you may want to specifically ask the dealer to check the threading on the filler neck.