It’s great to see how other people do it :)
A couple of differences from the way we do it here:
1. Our build directory is completely separate from our source code.
2. I’m lazier than you though and use a date/time string for my tag names .
Like you, I like having a deployment process in place as it makes the entire processes of putting a new version of a site live much much easier and stress-free.
Also, consider upgrading to ZF 1.11.5 :)