I have just download Version 4 (beta) and it looks good and is a tad faster on the scan, most of the changes are under the hood. A nice addition is the facility to repair the control panel - I like it
Scanning engine improvements to detect rootkits that keep handles open to themselves
Ability to remove most infections in a single pass/reboot
Improved trace detection
Windows Vista Scanning Improvements
Additional repairs for Windows Vista and Windows XP (System Restore and System File Checker (SFC)