IMHO, you shouldn't worry about bounce rate. Worry instead about time on site. In most cases it's getting at the same issue, but a better measure of success/failure.
That said, WHY the person leaves your site makes a big difference. If they left because they didn't like your site – that's a problem. If they left to go visit your sponsor and buy something – that's great. And bounce rate can't tell you whether it was a good bounce or a bad bounce.