ruby is really good for solving small problems quickly. Don't get me wrong, proficiency in your shell will go a long way. But when something starts to get complicated I can bang it out in ruby and it's just done.

Web apps do drive ruby's adoption, though. Now that I know ruby I use it for many things, but I learned it initially for rails. Many other languages (like python) can fulfill ruby's scripting usages (I would argue javascript can't - despite its many strengths it's just a little too awkward)