Windows 8 will have a new feature common to the entire OS and not just IE called SmartScreen that will dynamically prevent programs that have been deemed illegal, fraudulent or malicious from running (assuming you have it turned on).
While it’s not perfect (false positives and undetected malicious programs), this is a good step in the right direction, that uses crowd sourcing much like Web of Trust does.
Unfortunately, there are 2 things that I see that are wrong/missing from SmartScreen. First, by default, it’s not turned on. This just does not help most users, who are just not going into advanced settings to tweak anything – they’re simply going to use the machine’s defaults.
Second, it’s too black and white. It’s either ‘never run’ programs or do nothing at all. How about a ‘warn’ setting when a user tries to run an application marked by SmartScreen as dangerous?