In theory, being online should make planning a group event easier, but you can waste a lot of time on email or Facebook back-and-forth debating possible ideas. TheBestDay.com aims to streamline that process by creating a central location where you can ask friends to vote on potential options.
Developed in Australia, the site collates together the comments and votes and picks out the most likely option. It's a relatively specialised case, but if you're sick of picking through arguments on Facebook when planning group weekends or parties, it's a possible alternative. The webapp is free to use, requires registration.