I've just installed the IE9 beta (http://windows.microsoft.com/ie9) and noticed that AW doesn't seem to be registering it in my Browser Statistics.
Am running AW 7.0 (build 1.970) against IIS7/Windows Server 2008 logs
An extract of the log with the IE9 ua string:
2010-09-16 03:45:14 192.168.0.130 GET /mrtg - 80 - 188.8.131.52 HTTP/1.0 Mozilla/5.0+(compatible;+MSIE+9.0;+Windows+NT+6.1;+WOW64;+Trident/5.0) http://anthonyb.dyndns.org/ 301 0 0 405 4
The client machine in the above example was Windows 7 x64 with IE9.