I think social scheduling is not properly solved yet - mostly for me, this is either via facebook events (which is, I'm doing this, please show up) or email conversations (which get messy with lots of people). Like, I'd like to go out to the theatre with a good number of this group of friends - here are shows I'm interested in. This is when they're on (ideally event listing is provided via companies) Here's when I'm free. Here's what I'd pay. Collect that information from my friends and find a solution within constraints.

Also - could lead to a targeted-groupon like business model (in your circle of friends, 2 people have said they really want to come to our restaurant. Convince 10 people and get 20% off! Someone's friends that already like a product are probably the best word of mouth you can get). Or advertising could be much better targeted if you say what you're planning on doing instead of what you have done.

I had an idea like this once (and gave up cos I thought it was unlikely I'd pull it off - and I think I have a more reasonable idea to execute on) for a social-network travel agent. If you have hundreds of people giving you advance notification of their desires (I'd like to go skiing, for < £800, anywhere in the alps, with this group of people), travel agents could do collective purchases like booking entire chalets / chartering flights (a la Social Flights which also just hit HN headlines).