Grml developer Frank 'ft' Terbeck did great work for grml-zshrc to get better customization options for the zsh prompt. We just uploaded grml-etc-core v0.8.0 to our grml-testing repository and want to mention three blog articles by Frank regarding this new prompt feature:
The new grml-etc-core release also provides a rewrite of the way keybindings work. Please consult /usr/share/doc/grml-etc-core/NEWS.Debian.gz for further details regarding the new prompt and keyboard handling. If you notice any problems please report a bug or just show up in #grml on freenode and talk to us.