Forrester Research is offering a research report (priced at $195 US). The brief says:

“Macromedia’s, Microsoft’s, and Jaguar USA’s sites get rollover menus right. What’s the formula? Expose submenus right on the home page, as well as in rollovers; build delays into the code that opens and closes rollovers; and provide consistent visual cues and behavior.”

Basically, for two hundred bucks US, you get a two page (yes, you read that right, TWO PAGE) report telling you that rollover menus don’t work (ok, most of the time they don’t work). If you know anything about usability and functionality, or if you practice iterative design, this is a no brainer… on the other hand… here’s the info:

http://www.forrester.com/ER/Research/Brief/Excerpt/0,1317,33737,00.html