I've finally given up and made the shift over to Firefox from Internet Explorer, but it isn't Microsoft's fault...it's Adobe's.
Under Vista, some embedded Flash animations interact with the browser in such a way that the entire Aero interface freezes for anywhere from 30 seconds to five minutes. Using Process Explorer shows hardware interrupts shoot through the roof. It doesn't matter if it's Vista 32- or 64-bit. It just sucks.
It isn't that I really like using Firefox. From a usability standpoint, I prefer IE. But given how critical Flash has become to using the Internet, until this interaction is fixed, my browser has changed.