This is definitely not a particularly _new_ idea (I can't recall the name of the service, but there was one -- "Web 1.0" service if you will -- that existed a number of years ago), but I like this implementation. The plug-in, as opposed to a web-proxy method (which is what others I've seen have used), definitely has a more solid look-and-feel. As well, it'll undoubtedly work a lot better since there is no processing of the page involved. This isn't the type of service I would particularly use, but I can see the appeal of it.
Congrats on launching, I'm curious to see how you guys do.