Mostly too busy at the moment to do much about it. But it would be nice to convert a validator to run within Firefox. Looked at the W3C validator at one time, and it's written in C - not something that's easily translatable.
Problem I have with most of the validators is two fold. First, the external validators are hard to use in web applications (kind of a spinoff on Ben's suggestion about cookies, though I run a local web server off my box for development). You basically have to save off the page as an html file, put it in a publicly accessible location and then run the validation (I'll second Ben's suggestion of cut and paste HTML into a textarea for validation).
Second problem I have is that the validation doesn't usually look at the the DOM after the javascript cranks through. What I'd like is to verify the DOM at any particular point in time, not just at start up. I've got a bit of dynamic client side stuff happening that is invisible to all the validators that I've used.
Anyhow, Scrutinizer looks good. I assume you've written it in Smalltalk since it refers to Seaside?