Yes it is quite the dilemma. I know one or two people who are self taught and great coders. However, the majority of people I have worked with that are primarily self taught aren't good.
I guess the key to competing against diplomas is making separating from the herd - perhaps with pet projects, a blog showing your expertise, etc.
This seems a little narrow minded. Many highly talented programmers find a lucrative area and stick with it for a while, but they can pick up on the "new big thing" almost instantly.
IMO it all comes back to talent and drive which are almost impossible to judge in an interview but they tend to swamp all other factors over time.
As a high school dropout, I hate having to compete against those with diplomas. But I guess that's what I get for dropping out.