I personally don't worry about my baounce rate until it gets up to the 60-70% range. Even then it depends on what type of page it is. If it is amade for adsense page, a low bounce rate can be negative for your earning power. Frankly, you make nothing of MFA sites if they just read. The story is entirely different if you are trying to build a list per se.
for blogs or non revenue sites i'd guess 60-70 is fine, but as a commercial site i'd be seriously worried?