DM_Matt said:
...not particularly well...
I have to disagree here. It just depends on the group--the DM(s) and the player(s).
I am currently playing in one PBEM game which I've been in for almost three years. This group is finally to the point where the DM thinks he has a solid group of PBEM players: people who work well together, people whose characters are vested in the story, and people who can (generally) commit to post enough to make running the game worthwhile. It's taken a while (the first two years of the game) to separate the wheat from the chaffe, so to speak.
Another PBEM that I've been in for about 18 months is a "sequel" to one which ran for several years.
Both DMs have had experiences with people joining the game and then just disappearing (not posting); people turning sour on the game (for whatever reason); people who drop out and then months later beg to return--only to then drop out of site and stop posting , etc.
But both of these games are going strong, even though they've sometimes had a "lull" in activity.
One of the neatest things about a good PBEM is that the DM can post the story somewhere, and you have a good tale to spend hours reading! If you play-by-post on a message board, I would strongly advise posting the complete story on a web site somewhere. You don't want to lose that wonderful creation (the story the DM & players have built) to the vagaries of cyber-space!