Designers listen up, code isnt perfect thats why its poetry, getting your site validated might save you a long night of Redbull and Mountain Dew hyrbrid cocktails. Its always wise to make sure your site isnt a sloppy alphabet soup mess, and there are several sites that can preform the validation process for you at no cost what so ever, the only price of admission is realizing you might have to work longer hours on cleaning up some of the chicken scratch you have add to your site.
Now it generally takes a pretty good coder to clean out the garage of junk code, and I myself wear as many as 6 hats all at once, so I'm constantly covered in post it notes reminding me to validate every so often to make sure your code is clean enough that search engines don't treat your site like the red headed step child. I've used http://jigsaw.w3.org/css-validator/ tons of times and its helped out a great deal. Make sure you get that parking ticket validated compadres.