I've been both a Debian system administrator and Ruby web developer, and while I love developing in Ruby, I hate deploying it. In particular, RubyGems has a disturbing predilection for ignoring ideas like "the system owns /usr," messing with the package-based maintainability of the system. (RubyGems prefers to put its files near the ruby binary it's using, and doesn't make it clear how to change this or whether it's even possible. Then it encourages RubyGems self-upgrades.)
The usual recommendation to use RVM is great for developers to switch between Ruby versions and implementations (except when there are a lot of gems you always want in your environment). But that usual recommendation generally starts with "gem install rvm", which means you still need one working ruby and rubygems system first. RVM is also user-oriented, and (partly because of Windows vs Mac vs Debian vs RHEL vs .... issues) doesn't very well address system-wide installation. It also doesn't help the sysadmin who may have chosen a distribution in order to centralize maintenance issues in the packaging system.
These days I tend to suggest that Ruby deployments use JRuby, keeping the sysadmin on one side of the JVM and the developer on the other side.