I've operated startups for 10+ yrs and I still remember the single most useful feedback I ever got:

I'm doing a sales mtg for Invite Media and our angel investor joins to listen. After the meeting he pulls me aside and said:

"You are the worst fucking salesperson I've seen."

That was eye opening. And amazing, brutally honest feedback.

I am a lot better now at sales.

Because I was told honestly that I sucked and needed to get better.

So I'm going to try to be that kind of angel investor and tell founders they suck when they suck.

(and then explain why and how to get better...obviously)