The release candidate of the Application Compatibility Toolkit is here, and it's good stuff. I've had to resort to sniffing around with a debugger to find many issues with this one, and it's still improving for the final release!
I am particularly impressed by what the team has put together for compatibility evaluators. For those of you who are unfamiliar with the tool, you can deploy a data collection package (DCP) that does more than just collect inventory - it actively shims system functions looking for known issues that could trigger compatibility issues after a migration to Windows Vista.
One of these is the UAC Compatibility Evaluator. It looks for a more limited subset of compatibility issues than Standard User Analyzer or LUA Buglight, because it is designed to keep the machine performing well even in a wide deployment to real users. However, one thing to keep in mind is that the UAC CE does not detect issues for applications that are not run elevated - it only detects these issues when the process is elevated and able to succeed. (I expect this may change for v.next.)
Now, for the vast majority of you, this probably isn't a big deal. Most organizations will perform their compatibility testing BEFORE they upgrade to a new operating system, for fairly obvious reasons! However, one great use of the evaluators that I have been recommending is to install it in your test lab while you are going through testing. So, while users or testers are running through their tests, you not only gather their feedback on the behavior, but you have additional technical data that perhaps may showcase issues that aren't a big deal in the lab, but may be a big deal when deployed to a lot more people. If you choose to take this approach, and you want to gather UAC data, then you will want to either consider one of the more diagnostic tools or else run the application elevated (but don't forget test runs with it non-elevated!).