[JohnBoucher]

It's simply good practice to validate your code. Almost anything will render in some fashion, but the cleaner the code, the better the rendering. It also helps with your site being indexed.

Validation errors also tend to cascade. One error spawns multiple small errors. The validator gives lots of info on fixing the code.

I agree with rsisk, it's a judgement call. The reviewer can also give extra points if they think you deserve it. A site that validates html, css and Cynthia says deserves the extra points.

I had one last year that left a note in the code saying he did not care about validation.