Some of the secret details are in my theme:
https://github.com/davvid/oh-my-zsh/blob/davvid/themes/davvi... ZSH_THEME_GIT_PROMPT_DIRTY=""
ZSH_THEME_GIT_PROMPT_CLEAN=""
which lets it avoid expensive checks that my prompt doesn't need (it already shows that info elsewhere).
The real big win is that I export `POST_1_7_2_GIT=1` in `~/.zshrc` and the tweaks I made teach the git plugin to use `--ignore-submodule=dirty` when calling `git status`, which makes a huge difference.
I haven't caught up with oh-my-zsh in a bit; if there's a good place for me to rebase onto and do a new pull request I will. Does anybody know who the real oh-my-zsh maintainer is these days?