Holidaying is always better with friends, the downside being that the most organized person ends up doing all the work, and the most organized person is generally so boring, you barely consider them a friend. Making it easy for everyone to chip in, TravelStormer
Just launched in beta, Stormer's a London-based service that takes the pain out of group hols via collaborative tools for "decision-making and organization", keeping everyone from having to send "thousands of e-mails", while simultaneously shaming the lazy out of doing the equivalent of sending zero emails.
Users first start a "Brainstorm", basically a forum for overarching questions like "Surf or ski?", "Which casino to stay at?", or "Isn't marriage sort of outdated?"; then it's on to the Calendar, which can be populated with suggested events, as well as flight info, enabling you to safely schedule lavish dinners right when people might be needing flights from the airport.
Further organizational tools are provided by the Message system (auto e-mails your whole party, or selected members), Expenses (shows who's paid what for what, with a PayPal option coming soon), and Tasks, which details what needs to be done, and lets you make a member of the group "responsible" (hopefully this feature will become available offline by the time she figures out the child is yours)
Brainstorms can be made public on Facebook/Twitter (while still keeping private deets private), and votes for your final itinerary can be cast by family, friends, or even followers -- though if you're letting such tenuous relations decide your travel plans, the follower is you, and your friends are few.