One problem with a Play-by-post game is that you're stuck according to vagaries that don't plague face-to-face games. One of them is that people aren't necessarily posting at the same time. Games can lag for even simple tasks that could be resolved in seconds in face-to-face.
Another issue, and this has been plagueing me today, is server availability. Circvs Maximvs, where I run the "Demons in the Mist" game, has been flaky today, and quite frequently as I've tried to update it, I've found it unavailable. Grrr... One of the things that has made this game (so far) so successful was the fast pace. I'm concerned long term about losing momentum. These server issues, right on the heels of a long, weird, holiday weekend where folks weren't as available as they had been prior, is worrisome, as it can cause the game to slow down and never pick back up again as well as it had been.
Also; just a minor thing; I changed the settings so comments are now on a pop-up window instead of a new page. Maybe I'll get a few more that way.