Validating your site is a good way to see how your site compares against THE SPEC as handed down by the W3C. Validation isn’t the end-all be-all, but a site that validates will likely be “future-proof” and ready for that new buzz-word-approved technology that you’ve never heard of but will become vitally important next week.

Validation essentially makes sure that your site follows the rules. Theoretically, if everyone plays by the rules, then your site should look good in any browser that embraces the rules – even browsers that have yet to be released.

Check your site… Pick a page, the homepage is a good start, and run it through the form at:
http://validator.w3.org/

If you have no errors, then congrats. Your Web developer did you right. If you have just a few errors, then you’re probably fine, too. If you have 578 (give or take) errors, you may want to seek professional help.