Just stumbled across World66, "the travel guide you write". Basically it's like Wikipedia, but for travel destinations - I haven't done a thorough exploration yet, but what I've seen so far looks very promising. There's even a Mapsonomy section which is reminiscent of Mappr, but it links to the actual article about the location, not just photos from it. A powerful & logical next step would be to link World66 with Mappr. The thing I really like about World66 is its global nature, whereas Mappr is still only US-focused at the moment.
Where I'm getting at, of course, is location-based tourism! It doesn't even need to be 'location-based', per se. Basically, if you have a mobile device that can link up with a WAP version of World66 (kinda like the Flickr mobile site), then you can access all that wiki-travel advice. If you factor in the device's context-awareness, then I guess it could just automatically retrieve the most relevant entries & display them when the page loads? A bit like how Google.com automatically redirects to your country of origin.
Going one step further, you could easily link these caches of user-created travel/tourism data from World66 into some sort of digital graffiti system, like YellowArrow or Grafedia. Or adapt the info to be able to be sent over SMS. The opportunities are endless.
It makes sense that location-based services will have much greater value and be able to encourage quicker/more widespread adoption if it has a P2P/C2C collaborative content-building element. It helps that much of the collaborative 'infrastructure', if you like, already exists in the form of sites like World66 & Flickr. Why start from scratch when you can build alliances and tap into already-established communities of users and content relevant for your service?