Looks like a great service. I love the idea behind it. The design is nice, and wow, a site I can understand from the first view. Well done.
A few things I note:
- the home page presents the option to enter a URL for validating a site. That's a bit confusing when it'c clear this is a paid service. It would be good to make it clearer up front how this all works. I tried validating a site, and it worked, although the results were pretty thin on the ground. The few errors had no real explanation. Perhaps that's because this is a free check, but it's a good idea to make that clear, as otherwise people might not think it's worth paying for this service.
Ah, I see that if you click on the URL under the error, it goes to the W3C validation page. That's clever, but it's not obvious that this is what will happen. Rather than show the URL, it might be better to have text saying: "Click here to view detailed validation information for mysite.com/folder/page.html" or something like that.
- the other thing was that, while the validation was happening, it's not really all that clear if anything is happening. It might be good to give an explicit acknowledgement that the process is under way and that results will appear shortly, or something like that.
Good luck with this. It's a great idea.