Since you have quite long posts, I would suggest going to settings > reading in the dashboard and set your blog to maybe show 5 posts per page instead of 10. That will help quite a bit I think.
Secondly, go to settings > writing in your dashboard and select "WordPress should correct invalidly nested XHTML automatically" and then save. That will help to cut down on any HTML errors that might sneak in.
I just noticed that your blog is now reporting only 5 validation errors where when I first looked there were over 121, and Timethief saw over 500.
I would definitely say staff was perhaps updating your theme.