Official Google Blog: It's nice to share

"Now when I say “share,” I don’t mean “send group email,” and I certainly don't mean 'time-share'. (That’s actually the root of the problem we are trying to solve: multiple out-of-sync versions that are email attachments.) I do mean “use and update the same spreadsheet.” When I use Google Spreadsheets to organize events with the other parents at my kids' school, we’ll be looking at the same details at the same time. If I change the agenda of next Friday’s teacher’s meeting, the other parents will see that change immediately. When my brother-in-law’s bike club uses Google Spreadsheets to track rides, they’ll be in sync -- and if I change the time of next week's ride, the other riders may actually show up."