Jim Carroll:

"I wonder if peoples' objection to 'unsolicited' criticism also includes unsolicited praise - if not, why not?"

I've just explained what I think the problem is with unsolicited criticism! Can I quote myself?

"I think there's a real danger of criticism backfiring, however well-intentioned it may be. The effect on me has been to make me much more self-conscious about my singing than I ever have been before - when I'm singing alone I've fallen into the habit of pulling myself up, if I ever think I hear myself going off the note, and taking the line again. But worrying about what sound is going to come out of your mouth is no way to relax into a song - and if you're not relaxed you're much more likely to waver, falter and choke."

The effect on me has definitely been negative - I've been more nervous and more self-conscious & sung worse.