> One awesome thing this would allow is for people to create and curate special-interest travel guides.
I think there's HUGE potential in an online service that takes care of all the aspects of a trip. Right now you have the choice of either doing everything manually (which is a big time sink) or going on a package tour (which is bland and one-size-fits-all). In between you've got a few options like Expedia and Travelocity, but they're more like extensions of the package tour idea than a rethinking of the concept.
In my vision, you'd give it the dates you want to travel, where you want to go, your budget, and access to your social networking accounts (so it can figure out your interests/hobbies). Then it uses the data you've given it along with preexisting curated travel data (which could be based on crowdsourced info, both from previous customers and from 3rd party sources) to create an optimized & customized travel itinerary and take care of all the purchases (plane tickets, hotel reservations, Uber reservations from the airport to the hotel and between sightseeing locations (if needed), tickets for different sightseeing locations, etc.) so that you just have to pay once, to this service. You don't have to worry about when places are open/closed, how long it takes to get between them, etc. - that would be automatically calculated (should be pretty straightforward with Google Maps API access).
Then you'd want to have an associated smartphone app that will (in real-time) display the itinerary, give directions between the different places, suggest restaurants to eat at (maybe make reservations using OpenTable), etc. The itinerary could even be dynamic. For example, if there's an outdoor activity planned and it starts raining, it would automatically rearrange your itinerary as necessary, etc. You could use GPS and/or NFC at museums and other places to play back audio explanations of various exhibits (they already have this at many museums, but you have to pay extra for the privilege and wear an iPod or some other clunky device for the duration of the tour).