So, I installed IE8 on my machine at work. Initially, I was quite impressed. It seemed to render quite quickly (with the exception of CSS3 animation, which I kind of expected). On Microsoft-specific stuff, like Sharepoint, it actually seemed to be a vast improvement over IE7. The page renders were downright zippy. Interacting with Office Live Spaces was fantastic - the interface was very responsive and felt almost OS-like in its interactions.
However, I've had it installed for a while and it seems to be slowing down (exponentially, at this point). I'm not sure if the caching it does in the background is causing it to choke, but the responsiveness is gone and it's starting to feel like the same ol' MSFT bloat-ware to which I've become accustomed.
I'll update the comments if I figure out why it's happening.