Is "subversion" a skill (unless we're talking about spies ;)? It's just a tool. I've used it. I've used cvs, git and other stuff too. If I had for some reason to work in a company that uses some other tool to handle their code repos, I'd learn it in a month or so (less if it's organized logically). It's like saying "driving a Honda Civic" is a skill - driving is a skill, Honda Civic may be what you're driving right now, and next week you may need to drive a BMW, and being able to do both is what I'd call a skill.