Mystery Meat Navigation - don't serve It.
If there is one central tenet that should be followed in the design and architecture of any web site, it's clear and predictable navigation. That is the root of good usability. If you screw that up, you're toast and so are your web site's prospects for any success.
Vincent Flanders offers the most entertaining analysis of this problem in his Web Sites that Suck series. In reviewing bad web sites across the web, from Fortune 500 to smaller organizations, he has coined a term that pretty much sums it up - Mystery Meat Navigation.
In the words of Mr. Flanders, "One popular, but horrible, design technique is based on Javascript rollovers. It's horrible because you can't just look at the links and know where they will take you. You have to mouse over the links to find out your destination -- and that's wasted effort which will probably alienate your visitor."
So, take a look at your current site, if it's loaded with MMN, consider revamping it so that your users don't bail out on you before you've even begun your business with them.