I nearly got locked out of my own personal phone the day after setting it up to sync my calendar (not mail) from the Exchange server at work. The next day the phone prompted me for a password, but it didn't specify which one. It was obvious in retrospect, but at the time I thought it wanted the one of the SIM PIN codes or perhaps my Google account password.
It gives you 10 attempts; I finally figured out that it wanted the Exchange password on the last or second-to-last attempt. I'm not sure what would have happened if I hadn't gotten it right, but I'm guessing my phone would have been wiped.
The password prompt comes up every few hours now. It's a real impediment to usability, especially when the phone is first powered on. The phone is more or less nonresponsive for the first few minutes after the password prompt comes up.
It's a lot to put up with just to get my Exchange calendar into my phone, which contains no sensitive information.