IE8 no doubt has a lot of features packed in, both for the developer and the user.

Some of the front-end features are really impressive:

http://ajaxian.com/archives/ie-8-better-ajax-css-dom-and-new...

In particular, the ability to make XDR calls without using flash or other hacks is impressive. they also increased the number of parallel connections to 6 up from 2. The web is going to get busier for sure