I just know that whenever I wanted to use the official ubuntu repository, I ended up not being able to install a gem because rubygems was too old. Since gem update --system doesn't seem to work on debian-based systems, I just had to install it from source again
This wasn't a problem for a long time, but then a major release of release of rubygems came out, and then the switch to gemcutter happened, etc. I've gotten around this by installing everything but rubygems from the regular Ruby packages from the Debian (or ubuntu) repos. I install the rubygems.org version of rubygems and everything works great.
