This is an issue you'll find often in web sites. Let's take the Vimeo music store (http://vimeo.com/musicstore) where this morning I was reminded of this problems

Specifically I'm going to the Search box and look for “Chill out music”. Now just clicking on the search box, reverals the flyout, conveniently for me I see that it is a classic two-level flyout meny. The first level is a category. In this example, it is set to “Genre” and the seccond level a list of items in the category. Fortunately for me, “Chill-out” is already listed (highlighted in red below).
Let's see what happens:

And now the breakdown: I click on the search boc and see “Chill-Out”

Naturally intend I move my mouse as shown below.

As my cursor crosses the first level of the flyout – it selects another category.

Now keep in mind I'm not slowly moving the cursor – I'm making a very fast gesture that will bring the cursor to my destination in a fraction of a second.
The end result is that I have find my mouse where “Chill-out” used to exist on my screen.

This is an irritating pattern because, once a user figures this out they have to carecfully navigate the maze of the flyout as shown below:

A couple of things I want you to keep in mind.