I don't care about the disk space and RAM at all, but every additional C extension (like EventMachine) means one more dependency that can break when I update a) my OS or compiler, b) Ruby, c) Rubygems, d) Bundler or e) Rails. Most of these updates have to be installed immediately for security reasons. I absolutely love Ruby as a language, but with Rails I feel I spend half my time in the terminal, trying to fix `gem install` incantations just to keep things running :(