If your using MVC 3 and you have updated to the latest update just after MIX 11 then you may notice a very nice addition to the Scripts folder, something called Modernizr, at the moment my brand new MVC 3 web app has modernizr-1.7.js included.
If you wanna know what Modernizr is –> modernizr ?
Follow @Modernizer on twitter and even watch Scott Hanselman talk about it at Mix 11 Modernizer at Mix (Scroll to about 11 minutes in)