I downloaded the Beta some months ago - system instantly crashed. System Restore did just what it promises.
I downloaded the Beta again last month. Find it much better than IE6 and, so far, very stable.
The ONLY bug I have with it - and it may be co-incidence - is that I keep trying to remove a tool bar ("mywebsearch") that wife put on for me. Everytime I open a new window - there it is again.
So far, I really like IE7.