I post at SearchCommander.com now, and this post was published 18 years 1 month 9 days ago. This industry changes FAST, so blindly following the advice here *may not* be a good idea! If you're at all unsure, feel free to hit me up on Twitter and ask.
If you’re used to using http://validator.w3.org/ to try to validate your pages, then you’re going to absolutely FLIP if you haven’t seen this before – http://jigsaw.w3.org/css-validator/
Perhaps this tool has been around forever, and people who are “in the know” will wonder where I’ve been hiding that I missed it, but I don’t care. It’s SO useful, and just saved me SO much time, that I had to tell someone about it.
That said, is site validation really important for SEO? That’s another post…