If you jumped on a project and they used tabs and you used spaces, what would you do?
  
  issue :retab! command

Nice. So if you invite me into your home you wouldn't mind if I start to rearrange the furniture?

If you get onto some else's project or you start working on an existing code base, the polite thing to do is to familiarize yourself with the formatting conventions of that project rather than reformatting everything the way you like it.

To me, programmers who can adapt to an existing code base without getting anal retentive about tabs and spaces and what not, is to me a sign of a mature programmer.

  Can you describe the difference between progressive enhancement and graceful degredation?
  Bonus points for the answer “no one can”

Not quite -- the former is the technique and the latter is the objective. Semantics :)