Kudos to MS on the web browser update!
I believe this deserved it's own thread. Many of you know how outspoken I have been in showcasing the scripting flaws of the version of IE6 used on the ZuneHD. I used the full (not mobile or Lite) version of the Facebook website to demonstrate this. In 4.1, the website was slow to load, and would be very slow to respond to pinch to zoom. In 4.3, the website wouldn't even load.
4.5, however, is a different story. Facebook's full website now loads FAST. I think it may be faster than the Iphone/Touch now, and that's saying something. Scrolling and pinch to zoom is uber responsive as well.
Seriiously, MS, just add tabbed browsing (or simulated by adding more pages, like the Iphone), and a way to clear the cache (so I don't get red Xs after visiting a media heavy website), and you have a winner. This browser on a WP7 w/512MB of RAM could be a serious Iphone contender.