I agree with
stickyb -- there are a few cosmetic issues, but nothing serious. For example, the history sidebar doesn't draw correctly first time it's opened.
It's blown up once but, because I'd downloaded the MSIE Error Reporting Tool (get it from Windows Update) it fired the error off to Microsoft. Of course whether they'll actually do anything with it is another matter!
The personal toolbar is obviously in its' infancy and needs service providers to supply dynamically updated and interesting content; I imagine we'll start seeing these in about 6 months or so.
The single thing still missing? The ability to switch off pop-up adverts completely.