Just had another look at this SilkTide site that Clinon linked to. While it is probably very good for some things, I would not rely on it's scoring for design. I'll give what just happened to me:

I thought I'd try folkinfo.org/forum, not expecting (and didn't get) much. I was a bit surprised at my score of about 5 and getting the "faild Brittish disability lawa bt) for accessibility as I had build the new site to be HTML 4.1 compliant but found I had introduced 2 errors since (one unquoted attribute and on mistyped one). OK I fixed those and re-run and got a score of 9.3.

Anyway, I thought the previous "judgement" was rather harsh for what was wrong and thought I'd try mudcat/threads.cfm to see how that got dealt with as I know there are a few errors here.

To my amazement, it scored 9.3. Anyway, I went over to w3c and tried thier validator. With the 2 errors fixed, I got a pass for that page. I then tried the mudcat page and found it wouldn't really validate at all because it complained about a charater (which I would guess is in the user content) present not existing in the utf charater encoding it was using, perventing a proper error report.

Anyway, I changed character set and got a validation. I then tried different "doc-types" as one isn't given (itself an error as far as the validation goes) and the best I could get was around 625 errors reported. A lot of these are "repeats" BTW - an error in the html for a link to a thread for example would repeat for each thread, so it's not really as frightening as 625 might make one think.

Still, Silk Thread had given a pass! It doen't seem to be taking any notice of failurs that prevent a detailed error report from w3c but instead blindly gives the OK.