I upgraded a couple of my sites to 3.4 without knowing it was going to break some features. They still work in my 3.3 sites but in 3.4 when I try to highlight text and create a link, the link button does nothing in visual or html editing. I have to manually code the "a href" tag. I also noticed I can't click edit by the auto generated url and the url won't appear until I click save draft. Usually once I click out of the title and start editing the text, the title will appear and I can edit it to a better url if I want to. There may be other things like this not working but I've noticed these 2 since I use them frequently.