I was just now reading through the comments in the ask HN thread about a Facebook alternative and read a reply saying that there lacks a service that really nails event scheduling, which reminded me of an idea I've had for years now that I've yet to see implemented properly. I won't have time to do much of anything in grad school for the next 4 years, so hopefully one of you will find this interesting enough to implement, because I'd definitely use it.
The goal is to make the ultimate personal and social calendar. Events are suggested and committed to my calendar manually, via my groups/social circles, and suggestions from friends. The user joins a variety of groups, anywhere from his economics class group to the Justin Bieber fan club, and is also member of social circles that him and his friends have created - "school friends", "research team", etc. Each group/circle has their own page for group discussions, etc. Any time an authorized group member or friend in a social circle posts an event, it pops up on in the appropriate slot on my calendar. I can then choose to attend/maybe/not attend, comment, and share the event with others, all directly from my calendar. For every event that has occurred, an event page is created for photos/etc and only viewable by group/circle members. Now, I think this would be pretty huge if implemented correctly. The way I see it, the user logs in to their big calendar decorated in flashing notifications of new events occurring or being suggested. He/she also fills in personal events - "study in library"- and can organize his/her social life around that. Sharing events would be big too, I think.
What problem does it solve? Well, one thing I've always hated about Facebook is that it puts all my friends/acquaintances/etc on the same level, and that's not how it works. I want to rank my friends, be part of different social circles, because that's how I operate. With one group of friends I may act totally different than with another. And so a big part of this idea is giving users the freedom to create their own social circles, and define who they are by the circles they join and groups they're members of, and giving them the ability to plan their lives around that. I feel that more closely resembles how we act in real life. We attend a party with one circle, and go to the company dinner with the next, and there's little to no overlap most of the time; and a lot of the times we keep those two circles separate with a wall of privacy, for many obvious and various reasons. With this idea, you get that privacy, that control to choose which circles you're a part of, how to communicate with them, and how to plan your life around them.
I know this is something Google Calendar might be trying to accomplish, or what Kiko might have been intended for, but I just don't feel it's been done right. Socializr somewhat aims at doing that, but that site is crap - I've tried it. Biggest competitor is Facebook, clearly. Not sure how you'd position this properly to beat them out; I haven't thought that far ahead.
One of the problems I see with what you describe is the amount of management that I'd have to do in order to make it work, since I have different social circles that I need different privacy settings on and each have their own page for group discussions, and then you can choose attend/not attend, etc. For me, it'd seem like a lot of time and work I don't want to be spending organizing.