This year, the Vancouver Jazz festival added a new tool for all its attendees to use: a “Mobile Companion”, for the iphone (free, from the app store [NB: iTunes store link]).
This is probably the first (that I’m aware of) of innumerable related apps. I fully expect that every major, and shortly, even minor festivals, will have a similar app.
It just makes sense.
When you first open the app, after asking for your location, it’ll update with the current schedule, and present you with a screen like this:

If I click on an event, I get another screen with info on the show itself:

Of course, because your on an iPhone, the map is even more useful, because with 2 more clicks, you can directions to where you want to go, in the means of transport of your choice:

It would likly prove just as useful for single-venue events like Sasquatch, or Pemberton - live-to-the-second updates of who’s on which stage, maps to bathrooms/vendors, etc.
Give it another couple of iterations, and tying in these apps to things like twitter for real-time interaction will be easy, seamless and make it possible to interact with the larger digital realm. I’d love to see a couple more links on that Jazz Fest details page: This event on Twitter/Facebook/Flickr/YouTube/(whatever) that opens up a search results, in the app that displays relevant results, and perhaps gives an interface to contribute to it as well.