Interesting post and answers. We're very much a team, and experiences are as follows:
1) The proposal was for a huge game, and most of that has been mapped out, however having something "real", a product, helps, so we broke the initial proposal down into "chapters". The feeling was that if we had something working, something to show for the effort, then that would serve as motivation to continue. That sort of approach isn't always possible we know, but it worked for us. Essentially it was almost like an "Agile" project in terms of how we worked on it.
2) Sort of related to the above, when a member of the team would bring something in, everybody else would get excited about it. So if we had new graphics, or new music, everybody felt like they wanted to do more. I think we were lucky because whenever anyone said "I'll get the music for that done by next week", they actually did it!
3) We have a project manager acting as our team leader, but it's not about being pushy or "the boss". In fact he often said that he was just there to make things easier for us to complete, so the team were the boss, and the project manager removed barriers for everyone, and supported them. The PM was also able to identify everyone's skills and played to everyone's strengths.
4) Meeting in person made things easier. Some projects are done with contributions from all over the globe, but having that physical meeting, or at the very least a Skype call, helped tremendously.
5) It was fun doing it
6) It was fun doing it. Yes this is repeated twice, but it's really the key motivation for producing the game that we did.
Hope some of these comments help!