Has anyone had much success with multiplayer games over forums? I have really not experimented with it other than with Dwarf Fortress, but it seems that if we've got a knit group that has some of the same software, we might be able to do a "toss the save around" sort of game, whether cooperative or competitive, and it would work OK for people whose schedules don't involve setting aside multi-hour blocks to play a game the whole way through with other folks. The questions of course would be about game, style, and mechanism.

This would actually be really interesting. Any suggestions?

Just checking back up on this (because, honestly, I forgot forums below D&D existed). Dwarf Fortress is great for it, and Civ-likes can be interesting. Some games, especially older ones, have a built-in Play By E-mail feature. Other than DF, though, I've got next to no practical experience

I still need to check out Dwarf Fortess at some point, exactly how much of a time sink is it though?

Learning DF takes a few hours your first time just to get familiar with the controls and interface. Have the wiki and/or some other guide handy. When you get down to actual playtime, DF will sink about as much time as you allow it, from 15 minute bursts to "hm, I started playing when I got up and now it's dark. I think I missed breakfast..."