It seems a lot simpler to just type "git br" (or, heck, "gb") when I care. Usually I have a good reason for being in a particular branch, though I tend to check before doing merging anyway.

When I want to fiddle with minor configuration details, hey, bash and zsh users have nothing on emacs. ;)

It would be cool to do the opposite as well, don't start checking the fancy vcs stuff until 1/2 second after the prompt is loaded.

Agreed. I don't think Bash allows async function execution, though.