I got into UT online far too late, Only really started in about 2001-2002. After seeing lots of custom levels I had a crack at the UEd myself. I got a lot of great info early on which was lucky, and from there continued learning ever since. There were even a couple of people from the sites I look on that got jobs because of their abilities with map-making (One of them has maps in the UT2k4 original package I believe, havent seen for myself).
I wouldnt say that I know much at all about UEd cause there is too much stuff. But I do enjoy making maps every now and then (none of my work has ever left my hands), mind you I hate coding/programming (cause I can't do it, thats why I hate it
) Things like stochastic triggers, skyzones, dispatchers and movers didn't fit into this category for me, they were cool. It was more the funky stuff like changing the shock rifles blue beam to a purple or something for that map and then altering the pulse gun beam maybe. Even things like making single player enemies fall from the sky through creature factories and that is where I drew the line.
I also heard that mapping for 2k4 / 2k3 is different in that you need to make your own meshes or something using external programs (Maya and 3DSmax seem to be overmentioned)? and there is other stuff like anti-portals where UT didn't have them, it didn't need them. (Anti-portals stop zones through wals or something don't they, what an absolute pain doing that through a map?)
I fear that if I really went into depth trying to make maps for 2k4, that my head would explode. Then there is stuff like making skins.....