Cross posting since this board is more active: Provide your suggestions pls.
I expedited and got the passport in 9 days (thats not business days but regular days) and there was a holiday in there as well. I used a personal check and its cashing did not slow down my application. In fact, I had my passport in hand on the same day my check cashed through my bank and I was able to view a copy on line. How's that for service?
So no - I do not believe personal checks will slow down the application. Believe me the State Department has ways of getting your money if the check bounces.