I have upgraded to 3.4.1. I have noticed 3 issues:
1) The <!--nextpage--> functionality broke. The breaks all fell to the bottom of the page. See here: http://www.buckshappening.com/jamie-hollander-opens-byob
2) This gallery used to show up with 3 thumbnails across: http://www.buckshappening.com/happening-list-bash-photo-recap - now only 1. Looks... not great
3) The <!--more--> tag is not working in search results.