After some of the work I have done, especially with enjoying the site, here are a few things that did not pass validation:
Twittercounter : If you choose a certain counter code from the site to monitor your followers, the URL actually breaks the validation. I used the black counter and was I sorely disappointed. For a service uses by many, I would think this site owners would consider giving a code that would not break.
Twitip ID: This plugin is designed for WordPress so that anyone who comments on your site who is also a Twitter user can put their username. The code breaks in the form attribute label that is suppose to be manually inserted. The creator of this plugin is also the creator of Commentluv, so I am not sure how this ended up not validating as the Commentluv passed. Andy, please fix it or I will very soon myself.
I would love to use these tools, but being a bit of a code stickler, I cannot use them. It is disappointing as these are both very popular tools.