Whilst I was writing the above, I recalled a more pointed answer to your secondary question -

It's probably not quite the kind of "doubt" you reference, however Max Levchin at Startup School recently referred to having a scintilla of such towards Peter Thiel when they were first kicking off PayPal. This doubt was engendered after Max was abandoned in a carpark with an empty car battery by Peter who seemingly didn't really care too much for his welfare (I personally wouldn't consider Max referencing a deep-seated sense of doubt, but maybe that's all that you're referring to)... I think by all measures, things worked out fairly well thereafter... ;-)

If you haven't watched/listened to it already, worth the time for the above and other amusing anecdotes/morsels of wisdom: http://www.justin.tv/startupschool/b/298808490