Emacs 24 is said to come with GTK3 support. What difference will this make (for the users)?
Function wise none (except it might be easier to use for people with disabilities) but esthetically it's a little bit better. I don't know of any drawbacks when it comes to GTK3.
http://batsov.com/articles/2011/08/19/a-peek-at-emacs24/ here is a good list of the new features.
Screenshot of Emacs 24 (GTK3):