I also think that if you put in a "good faith" effort to do the right thing and have a good relationship with the fellowship directors, you can get out of verbal agreements. However, it's the person who has an attitude that he/she is "entitled" to the best position and doesn't care who he/she has to **** to get there is the one who leaves a bad impression and will be talked about for years to come and may even have issues when it comes to future employment. I've seen residents who took a position at program A outside of the match who then try to go on to find a position at another program without telling program A - if you are discrete, it's fine - but many PDs - mine included - would get VERY upset if they found out. Same thing with fellowship - if you already took a position at a fellowship program and you are still shopping around, it may get back to the original fellowship director. I've been to meetings with fellowship directors and antics of certain applicants were discussed and many fellowship directors and even the program coordinators knew the few applicants who stood out for trying to do some sneaky stuff.
I'm not that naive that I don't know how competitive it is out there and how the fellowship directors definitely have the advantage. i also know that there's some dirty stuff that people pull. I don't think the process will be improved in the near future - especially until the dust settles after all the ACGME requirement related changes. So I think ppl should do what they feel comfortable with - my comfort level may be different from other people - I just like to form personal relationships with people and screwing people over never seem to help make friends.

it's that saying
"don't **** in your backyard" - if you can foresee future interactions with fellowship directors and those associated with fellowships, then you probably shouldn't do anything you may regret later. If you are going to move out of that backyard and go play in another backyard (neurosurg, ortho, etc.) then perhaps, you can **** in your present backyard and get away with it. You're just making it difficult for future grads from your program - but then again, that doesn't necessarily effect you, so who cares, right?