The problem with most menu systems is that they’re really touchy whether you’re too fast or slow with the mouse. The trick is to use a timeout with the effect, so it will wait a fraction of a second to pop-up, and a fraction of a second to go away…just enough to make the effect feel solid and not finicky.

Website: http://www.pjhyett.com/articles/2006/07/05/timeout-your-mouseovers#