I, too, am one of these people without a degree who has occasionally gotten a bit of flak for it. In general, I find that the people that give me this flak are those with degrees who have wasted 4-8 years of their lives obtaining said degree.
Let me elaborate a little further.
I failed algebra in high school. Shortly thereafter, I decided high school was a waste of time, and dropped out. I started college. After 2 years of that, I got a better offer. Work, and support myself full time, or go to college, and incur debt. This was an easy decision.
I still don't really understand math in a pure sense. However, in the last month, I've been required to "learn" set theory and pieces of calculus through my job. In fact, the only way I ever came to understand Algebra itself was in terms of programming. My professor was very understanding and allowed me to use programs I had written to solve equations on tests.
So now I'm 26, and I have almost a decade of experience under my belt. The last time I was actually hunting for a job, it was because I was unhappy with the job I had. I found a new one, and was prepared to leave when my current employer offered me a 20% raise. I realized at that point that the only implication of that was that they had been paying me 20% less than they thought I was worth to somebody else. This, too, was an easy decision: I took the new job at a slight cut, knowing they wanted me for who I was and what I could do for them. I'm generally much happier with this employer.
Whoever is giving you guff has (usually) one of two reasons:
Don't let it get under your skin. If you're where you are, and they're where they are, you have a definite competitive edge. Don't let their insecurity rob you of that.
and no, i'm not bitter. not even a little.
Tilly is my hero.