Location-based advertising? You've seen that, right? Practically every other ad you see on the net is tied to your general location, which is derived from your IP address.
"A user checking Eventful’s site for the next Coldplay concert in New York City would see an ad for Scion with the address and link to the closest Scion dealership, while a user looking for outdoor activities in San Francisco would see a localized ad for Subaru."
Now, I'm not a particularly big fan of ads (who is), but this type of advertising might actually be useful every now and then. How do they do it? A combination of user-entered ZIP codes, content taken from Eventful and GPS for mobiles who have it, for example iPhone or Nokia N96.
Placecast has been integrated across Eventful’s entire online advertising inventory and email programs, and it delivers all kinds of ads (text links, Flash, images, video, audio) on any connected device, such as a laptop or a mobile phone.