This is definitely one tool you should be trying if you're writing web apps with Visual Studio. Cross-site scripting bugs are one of the most frequent classes of security issues in web apps, and as such any tool that can help you identify and remove these before you take your code into production is a very good thing:
One of the biggest, constant problems we've seen our enterprise customers deal with and we here at Microsoft have to also contend with is that of the XSS (Cross Site Scripting) bug. It's very common and unfortunately, still an issue we have to deal with in many web applications. Internally, the ACE Team has been working on several projects to help mitigate and fix these issues, as well as detect them in the code bases that we review so that they can be fixed before going live.
XSSDetect runs as a Visual Studio plug-in and can detect potential XSS issues in managed code.