In my experience those who are overwhelmingly confident do just that, overwhelm. I'm presently in a long term relationship (1 year, woot!) and thats mostly because (apparently) I was confident to start with (which is, in all honestly, a side effect of being shy -- making jokes, up for smalltalk etc.) but was very shy when it came to actual relationship issues. Its apparently endearing.
My best advice to anyone curious on the subject is literally, and cornily enough, just be yourself. If you're yourself then its all good but if you're not you have to put on an act and it sucks. Plus those who don't have the 'confident' vibe about them naturally when trying to pull it off artificially tend towards being offensive and irritating to those he or she is trying to impress.
Just my 2 pence, there.
- r_o