I just hit the same issue, and I started using desktop-save-mode for that (https://www.gnu.org/software/emacs/manual/html_node/emacs/Sa...). It may be a bit heavyweight for instant switching, depending on what you want. I found it among a list of possible solutions at http://www.reddit.com/r/emacs/comments/1m73gs/how_do_you_man... .