I used to have the one character per game, but it caused some issues. Some people had real life issues and as such had to put their character on hold or such. If that character was central to another character it affected the other player. I then opened up to more than one character so that they could essentially keep going in the game while waiting. I imagine there are other ways to accomplish this - such as coming up with a logical storyline for the character, but it just got easier to create characters.
I would love to run a game where everyone was 100% invested in the game and posted at least every other day. I just am not sure how to accomplish this. Even the most creative games seem to get slumps.
I know what you mean about getting people 100% invested (or at least dedicated enough to post that frequently.) It doesn't seem to happen a lot here. I guess one of the big benefits I had was that when I created my other forums they were dedicated to MMORPG's (pre-launch) so people were excited about the game and already eager to invest time. So we played with daily posts for months and months at a time before game launch (I assume the forums died at game launch or close to it - I don't know because after running them for over a year I handed them over to someone else.)
As for the "player not posting" and holding up the game. This is a reason why any game I've ever created there was a stipulation that if a player didn't post after X amount of time, I would NPC their character out of the scene (or out of game if needed.)
However, I also see that if you have a mix group of rapid posters and slow posters it's easier to just let the fast posters have multiple characters.
For a one player = one character game:
I think my ideal posting situation would be a minimum 4-5 days per week (Minimum 1x per day). That way people can take a few days off and are only required to post once on each of those days. Giving them freedom to work on other projects/RP's if desired. However, the posting regimen would be strict enough to keep participation/activity high. (Coupled with the stipulation that if a player/character doesn't post after 3 days they get NPC'd out of the scene. Also if no posts after a week they get NPC'd out of the game - unless a PM/post is received stating that they will be away for some reason or another.)
I almost would like to try an experiment with a higher minimum # post limit just to see if I could actually get people to play it - see if there's interest in that sort of thing.