Which tool(s) do you use to install/upgrade your app on production?
__david__:     darcs push

which sends patches to the test repo and    ssh remote darcs --repo=live pull ../test

which is in a makefile so we can just do:    make release

Let me add here that darcs' inherent cherry picking abilities are a wonderful match for web development. Being able to fast track changes to the live site with no hassle is heavenly.