I love simple. If I can do something in a simple way, that, is the way I will do it. Releasing new features, updates or upgrades of sites can be a PIASS, even when you use the whole shebang of version-control systems, release-management environments and what more.
I think it can be done very simple (okay, I don’t run bank-applications that are critical to the world economy, but still) with symlinks.
Say, I have a tool called “foo” that gets a critical update.