Have you tried adding :
addthis.toolbox('.addthis_toolbox');
addthis.counter('.addthis_counter');
addthis.init();
or something similar in Infinite Scroll’s “Javascript to be called after the next posts are fetched” under settings?
What a splendid idea! It has seemed to do the trick too. Most of the errors were just poorly formatted text, many repeated in each blog entry. It’s still not validating 100%, but the remainder are due to facebook and addthis code. The sidebar floats correctly now. Thanks!!