Howdy Dharmesh. I think it's a cool idea--good luck with it. I like the http://www.websitegrader.com/ app. I ran it on a couple sites I'm involved with and got some good suggestions.
Thanks. This is a pet project of mine (amongst others). Response so far has been pretty good. We haven't officially "launched" it yet, but about 9,500 URLs have been processed by the tool so far. It's a fun little tool to work on.
I hadn't seen the site before, very cool. My only suggestion would be to offer the necessary syntax when relevant, e.g. for adding meta keywords. Granted, it only takes thirty seconds to lookup, but people are more likely to make the changes immediately before they forget if it's right there.