It has certainly boosted my confidence in that I now am able to use a mic publicly and I rarely falter with it. Before, I would freeze and end up saying a lot of "umm.... uhhhhh...".
I know my singing has improved over the last couple of years, though I know I'm far from fantastic. Use it or lose it! Confidence in singing makes a HUGE difference, even if you're not all that "good" at singing. Sometimes i think half the battle is having confidence.
As for growing a backbone, I'm quite the opposite of Babs. I've learned to be a little more lenient and have learned much more patience (I think!). I've learned to "loosen up" a little.
I've also gained some great friends I never would have had otherwise, since I don't go out these days unless I have a specific reason, karaoke being one of them.
Great topic, BTW