I have been using the beta I.E. 7.0 for about two weeks now. It is interesting to see how this version of the browser works. Microsoft has done their homework in this upgrade. The major changes that I like are: Tabs, settings, and Favorite groups. There are a lot more items that are nice, but those seem to be the major ones.
A few things are still not working quite write with this version. When I use MS visual studio 2003 and run my web apps in debug mode the http://localhost does not render on the first load, you have to hit refresh, even though I added that location to trusted security. I have also noticed that a lot of textbox areas on web sites do not function quite right, there are issues with the backspace. And the one major issue I have is the lack of right clicking on a link and opening in a new tab. I have seen that option available on some links, but not all.
Overall it is worth the upgrade. I was using FireFox almost exclusively for browsing and IE for development. The reason for using firefox was the tab feature. I like to open a lot of sites and then eventually get to reading them.