Twitter Bootstrap не проходит валидацию W3 CSS?
Валидация - это не показатель. Она изначально не поддерживала многие фишки стандарта и сейчас не поддерживает.
На выдачу это никак не влияет. Вот слова инженера который занимается crawler'ом в Гугле:
"So Google does not penalize you if you have invalid HTML because there would be a huge number of webpages like that and some people know the rules and then decided to make things a little bit faster or to tweak things here there and so their pages don't validate and there are enough pages they don't validate that we said OK this would actually hurt search quality if we said only the pages that validate are allowed to rank or rank those a little bit higher."