I was very pleased to see that my posts are actually HTML5 compliant.
The validation is specifically for my “How to make a simple Waterfall chart” post.
I genuinely believe that in the future that code segmentation/html5/microformats are going to be really important. Especially for e-commerce large sites. If there is only so much PageRank to go around, and this means the depth and aggressiveness of crawl, you need to make it as easy as possible. That way they can prioritize and understand what you have available.
In terms of the validation. I think I have to give all of the credit to the theme team. But at least I haven’t broken it. And I only had to turn off one plugin that wasn’t compliant (and my edits broke it) to get there!