Code validation is an issue that has been tossed back and forth in the SEO world for years. The W3C's standards appear to have the general support of the validation and standards organizations across the Internet, thus leading SEOs to ask the leading question,

Does having validated code help with search engine rankings

The general consensus on the issue has been a resounding NO. Authorities from every forum, SEO company & private sector appear to agree that search engines would be remiss indeed to reward W3C valid code. However, many SEOs have noted that the advatanges from having valid code are worthwhile, regardless of rankings. The most prominent among these being that search engines can understand exactly what your page is trying to say, without getting confused.

To check your own code for validation, visit the W3C's HTML code validation tool.