Thanks, guys.
I suppose while I've got this open I should write something about mapping, like I said I would a few weeks ago.
4e D&D is a very tactical game, and some kind of combat map is a must-have, IMO. It doesn't have to be fancy. For Hoofchew I deliberately used a simple mapping system with no external software or image editing, just to show that you don't have to be a mapping wizard to run a complex fight. The Hoofchew map was fairly detailed, with multiple levels, difficult terrain, obstacles, cover, etc., but the map was really not very much work. And the learning curve for old-school code-block mapping is almost nothing; you can make the map in Notepad and paste it inside [ code ] tags (without the spaces).
On the other end of the spectrum, you can use image editing programs like photoshop or GIMP to compose the map. You store the master copy of the map in your image editor's native project format, with layers and whatnot, and export it as your favorite image format, perhaps PNG or JPG, when you want to make a snapshot for players to see, and upload the picture to somewhere on the internet. It helps if you have your own reliable place to host images; you can put images up on enworld itself, but there's a limit to how much disk space you can use that way.
I did that for a while with GIMP. It takes a lot of initial work to get your map set up properly, but once you do, you can do lots of neat things with it that you can't necessarily do with other methods. Of the mapping methods I've tried, this is the most work, but if you've got mad skillz you can get the best looking results this way.
There are a lot of options between those two extremes. I'll cut to the chase and tell you that I'm currently using maptool from
rptools.net. It's not directly intended for PbP, but it's free, has good tutorials and a strong community, and it's easy to find links to lots of free backgrounds, tiles, tokens, and mapping objects made by other people who can actually draw. Which is nice for me, since that's a talent that I entirely lack. If you follow the "My Games" link in my signature and look at the Monster Mash games, you can see some of the recent maps I've done with it.
As for running combats themselves, I think the most important things for a DM in PbP combat are to keep things moving, and to provide a complete, accurate summary of the current situation at fairly regular intervals. Obviously you have to interpret the rules too as you go, but to be honest, minor rules mistakes during combat don't really interfere with The Fun. In fact, over-rules-lawyering in combat, a temptation I often struggle with, can often be quite harmful to The Fun. Keep the action moving, and communicate clearly what the situation is. (A good map helps, of course.)
One of the things I really like about 4e, that means that I have more fun as a DM than I did in 3.5e, is that death isn't that big a deal for PCs. It's not pleasant, but it's not career-ending, either, like it usually was at low levels in 3.5. That means I can take the gloves off and really play the monsters to their full tactical potential, doing my best to win. Of course that only applies to running the encounters; when designing them I still want to make sure the PCs have a good chance of victory most of the time, balancing challenge with fun and the needs of the story.
Next: random observations about DMing in PbP and how it differs from tabletop.