I have been using Beta 2 of IE7 for almost a week now. No major crashes and it is quite stable. No major changes to the UI compared to the Beta 2 preview. I think the new list of open tabs is appearing as a dropdown menu near the Quick Tabs is new though.
The major irritant for me in this release is the changes made due to the law suit relating to the ActiveX controls.
Polaris uses Lotus Notes for mail and its web access if built on Java. The change forces you to click the Applet/ActiveX to activate it. So now every time I need to write a mail, do near enough anything with my mail, I have to click twice to do it. There currently is no way to actually turn this feature off, the only way is for the web page to be modified by the web owner.
And ofcourse, this affects all Flash web sites too as Flash currently runs as an ActiveX.