Hey there, how important is it to have a w3c-valid website? My website does have pretty much errors (810), but most of them can't be fixed properly because of the different browser problems. How much will this affect my SE rankings?
W3c validation and good rankings is just a MYTH I never w3c validated no site but i got to first page in the past 6-7 years over 800 sites
if you have a lot of errors on your site, mentioned by W3C validtor, you may ahve affect your google rankings. Why? Because many errors cause a low speed page loading, and an important thing considered by google is the page speed.
W3C badges are only to show off. But one I thing I like to say that If your site contains tooo many errors then obviously Google may penalize your site. So its to check your site whether it is giving several hundreds of errors or few. It always good to keep the errors as low as possible.
It's just a cool thing to know, that your website is 100% valid and that you can show the badge Google might care about the speed, but I don't think that validation errors have any impact on the ranking...
Besides the speed and accessibility issues, you also have to make sure that any html errors on your page do not make it difficult for the search engines to crawl and parse your site properly. Matt Cutts from Google recently addressed this question. http://glendaledesigns.com/news/103.html
Short answer is NO it doesn't effect your search rankings directly. However, as the number of websites is soaring it wouldn't be unbelievable that Google would eventually start taking it into account as PR and other factors keep getting abused.
In my opinion Your website is an online representation of your business. This makes it essential for your design to render correctly on the screens of your customers without any glitches. While choosing a web designer for your site, you should ensure that he adheres to the W3C standard.