A WebmasterWorld thread has a horror story about how difficult it seems to take PPC data out of Yahoo! Search Marketing and port it to another account. In this particular case, the person is trying to detach from a search agency and migrate the information elsewhere. Is it possible?
It seems that the answer to that is no.
Werty speaks about his own experience with his switch over to Panama. According to him, when that happened, one of his clients had master account privileges to all his other confidential accounts of his clients and in the end, there was a huge issue with trust. It doesn't seem like the issue was resolved to his satisfaction.
In the end, then, it seems that YSM still needs to iron out a few kinks: one, in security, and two, in portability, in order to win over and maintain more potential advertisers.
Forum discussion continues at WebmasterWorld.