I know very few people using the distro version of Ruby in production. Most are using either rvm (not so desirable) or a custom-compiled version (more desirable).
In my experience, the version of Ruby shipping in most Linux distros and package systems is outdated or less than ideal for production use.
Apt-pinning and source packages are great ways to bring newer Ruby in to Debian stab
The first thing I did after you left our common former employer was ditch all of the manually-installed REE on Ubuntu and changed to Debian stable with .debs of ruby and rubygems pinned in from testing. It was an improvement.
+1. Many programmers who are not admins tend to install stuff according to their one-time desire and then announce it "production ready". In fact, there's something called "release management" and it's a rather different mindset. Please coders, respect your admins (and vice-versa), or learn to play both roles. Tools like rvm, while cool, are not substitute for this, because they can create an illusion that there's nothing to learn. There is.
I'm not familiar with the technique you're referring to, is there a reference you could point me to that discusses "apt-pinning" packages from testing? We recently had a "there must be a better way" moment trying to get a standardized Ruby 1.9.2 installation set up - I think what you're describing is that better way.
In my experience, the version of Ruby shipping in most Linux distros and package systems is outdated or less than ideal for production use.