* The paginated loading of HTML/CSS validation does strange things with the loading bar. I was trying to drag it to the bottom, and it kept moving itself upward as it loaded new pieces. Doing the deferred loading is cool, but it would be better to kick it off async and have it run to completion, versus waiting for scroll-per-page.
* In the downloaded report, there's no indication of what the grey circles are (average top-1000 result).
* Detected Technologies is odd, it only lists comScore for the site I tested - should that include Google Analytics, Facebook Graph, etc.?
* The Table of Contents isn't clickable to get to the related sections.
* The color-coding of sections doesn't mesh mentally with the counts presented. I have something in green (Success) with 7 tips, and something else in red (Issues) with 7 tips as well. Is that good or bad?
* I didn't check the "short" report option, but I'd like to see just things-to-fix in its own report, with details of how to fix them. As-is I have a 35-page report with no clear indication of what the biggest problems are, just the biggest per-category. I realize the webpage already does that, but unless I'm the sole developer I would want to send a hit list out to my team as a PDF.
* Your own page is only 99 out of 100 =)
All of that aside, this looks really useful. It's like a prettier version of http://www.webpagetest.org/ - a lot of the same info, but a much better / more modern presentation. A good pricing hook might be a free (scheduled) report once a month, with the top-level warnings included but a paid option for the full detail.
Good luck, and congrats on "SHIP IT"!