One of my apps accesses a persons' contacts. The approach I took to this was to notify the user ahead of time that I would be asking for permission to use the app, and that we would never use the contacts for anything but in app convenience. It feels great and is very informative. Only thing is the code is a bit wiry, but I'm working on that.
I'm convinced this is the best way to do it. I was testing one of those apps that repeats what you say and they did something like this. They popped up a dialog that said, "We are going to ask for access to the Microphone. We need this so we can make the animal repeat after you." When you tapped "OK" the permission dialog popped up. Apple should really let the developer put some information like that on their permission dialog.
Yes, they do. Many apps use them (including the one in the linked article, which shows customized usage descriptions in their screenshots). The documentation I linked applies to both Cocoa and Cocoa Touch, and you can see whether OS X or iOS or both supports each key based on the Platform column on the right.
That's a great approach - specifically reassuring the user that you're not going to do anything malicious with their contacts. 95% of the time, if an app requests access to my contacts, I will deny it fearing that it's going to spam them text messages like "Dav- is using ShittyFooBarApp – Click here to join them! http://spammy.co/ad9s8hu".
