What Linux distro for a Rails app that needs to scale?
tialys: Debian.  It's what Ubuntu is based on, but it's less crufty.  I use Debian for everything I do, and I've never had a problem.  Take my advice with a grain of salt however, as I've never really had to scale anything.One other thing, make sure you build everything from the source.  Get exactly what you want/need, and nothing more as well as the latest packages.