HoverIntent. You Need It.
I've been using a commercial product at work that has a jumpy and annoying menu system in it. Every time I use it, I only think one thing:
"They need some HoverIntent"
HoverIntent is a jQuery plugin that extends the "hover" event into something much, much better. It's become a really standard tool for my pages and any page I encounter that isn't using it and uses a hierarchical menu (such as the product initially mentioned), it drives me kind of nuts.