I spent more than a bit of time on a variety of websites in desperate search for a Nintendo wii for my son's birthday this past weekend. That effort was fruitless, but I also found the UI of many of these sites was driving me out of my mind.
There are some great applications of mouseover effects, but it's being overdone, and not in a considered manner. I'm pretty darn good with a mouse, but I often found a popup obscuring what I was aiming at in the website's zeal to provide me with dynamic content. I'd hate to think how my mother (who frequently calls with "I lost my toolbar" kinds of mouse accidents) would navigate these sites.
Just because we *can* do something technically doesn't mean we should do it everywhere!