I'm a programmer in Massachusetts, though my academic training was in theoretical particle physics. About a decade ago, I wrote most of the Black Hole FAQ referenced in the featured entry on black holes; this was actually part of the Usenet Physics FAQ, which is one of the best online sources for unraveling frequently-encountered puzzlements about physics.
I'm fairly new to Wikipedia and just learning the ropes. I started in September 2004 as an anonymous contributor at IP 22.214.171.124 with some small-scale edits concerning old-timey motion picture devices.
My first big contribution under my own name was a series of expansions and repairs I did on Antiparticle; I then did some work on Path integral formulation, with much entirely new writing, much material that I imported from the former article on "Functional integration (QFT)" (mostly by Phys), and a diagram. Both of those articles still need some work, but I hope I improved them.
I think I'm getting better. Lately I helped greatly expand Asymptotic freedom in celebration of the 2004 Nobel Prize in Physics, which went to Gross, Wilczek and Politzer for discovering asymptotic freedom. That led to a major expansion of Color charge (though now I wonder if it was entirely wise; almost all of the subject matter overlaps with five or six separate articles elsewhere in Wikipedia; but it's still nice to have it in one place—maybe the ultimate answer will be to reorganize a lot of the material on quarks).
Recently I fulfilled what seems to have been a long-standing demand of several people, me included, and wrote a real article on Renormalization, replacing the previous redirect to Renormalization group, which really wasn't enough. My bid to make it a featured article was unsuccessful because it was too abstruse; I see the critics' point and hope someday to rectify this, but it's a difficult task—as others have remarked, what's really required is a specific feat of science popularization that, to my knowledge, nobody has ever successfully achieved, in print or online.