usage of common js libs

[Justin Collum]

I'm thinking of building this site. It'd be free to use (probably donate ware / twitter-ware ( http://www.paywithatweet.com/)). 

It'd be a site where you can see the prevalence of particular js libraries on the web. Say your thinking of using yepnope.js to implement a fallback feature. Well, how common is yepnope? Will the typical user have to download it if they've never been to your site before? Or is it common enough on major sites like linkedin or facebook that you can use it freely, knowing that there's a damn good chance the end user will already have it? 

My question: does such a thing already exist and I'm not aware of it? I don't want to rebuild a wheel here. 

[Scott Hanselman]

I thought about this some more. I'd want it to look like this  http://microjs.com/#  but have usage data to help make the decision. Make sense?