I (finally) posted a release for Valkyrie yesterday. While still a work-in-progress, our team (at Poetic) has been using it for months in our entirely features/git-based workflow.

I built Valkyrie based on much of what I'd learned building drush-vagrant/aegir-up. It's a little less ambitious, in that it drops the concept of "blueprints", in favour of building a bunch of re-usable components. It solves NFS permissions/ownership quite nicely, and provides automatic domain resolution via Avahi mDNS (on Linux) or vagrant-dns (on OSX). Did I mention that it's battle-tested on both Linux and Macs?