Coworking, coworking, coworking.
Everyone should be part time at 2-3 places. Couple hundred bucks a piece and you rotate throughout the week. The benefits of connecting with the community therein; hiring, finding partners, business development, networking, etc. are invaluable. But that doesn't answer your question....
Teams of 3-4 people can and should be working this way. Work from the same place once and a while, spread out and work in different places on your off days. Depending on the business or service you provide, I've heard of teams of 20 working throughout a city in coworking spaces (design firms, development shops, etc.). Imagine how quickly those companies established their brand and developed a sales pipeline when they are located in every shared space in the city?
When should a business or startup needing to spend most of it's time together really have an office of it's own? At least 7 people. I really believe that it's the size that matters; more than the reasons you believe.
We're hiring developers overseas, marketers and sales professionals throughout the country, and executives who's commute makes working with you prohibitive.... don't be fooled into buying Silicon Valley's mantra that you have to be in one place, be there, to be more successful. The tools and technology exists today with Podio, Skype, etc. that the reason you need to be in the same office is that there are so many of you that being distributed is no longer feasible and the opportunity cost consideration, of having your people all over town meeting, networking, and evangelizing your startup, changes.