The good people at PC Mag have gotten their hands on the Vista SP1 Beta, and are apparently quite pleased with it.
It seems that the performance and responsiveness of the overall system is obviously increased. The time taken to wake a machine from hibernation along with copying and extracting files has been noticeably reduced.
A couple of security enhancements have been made as well including the ability to use BitLocker on secondary hard drives, signing Remote Desktop files, the addition of Secure Socket Tunneling Protocol and the ability for anti-malware software to extend the 64-bit kernel.
The only issue reported in the review was that upgrading an existing installation of Vista didn't install properly on one of the test systems.
Continue reading for the full review...
Microsoft Windows Vista SP1 Beta - Review by PC Magazine