Buying in bulk is a staple approach to saving money with physical goods. OurDeal offers a similar approach to "experiences", with daily discounts on meals, sports and other activities if enough people sign up for a given deal.
OurDeal is entering a somewhat crowded marketplace, with both JumpOnIt.com and Ouffer.com providing similar services that use the "if enough people buy it, we all get the discount" metaphor. That's not a bad thing if it means a diverse choice of deals to consider -- the risk is that, as with gadget deal of the day sites, every one of them ends up selling discount pedometers.
That said, so far OurDeal seems to have had a decent mix of dining and recreation offers. Currently the service is operating in Sydney, Melbourne and Adelaide, with other cities to follow.