I got my International Driving Permit today. 
It’s a boring slightly-larger-than passport sized booklet. It’s $15 at AAA (no membership required) bring 2 passport-type photos if you have them, they’ll charge more if they need to take your photo. If you go in they make it up and you take it with you; you can mail in for it also (a list of the 180+ “participating” countries are on the application form). Make sure they check all your endorsements on the form before you leave; they forgot to check my motorcycle endorsement (I noticed before I left).
When you travel you still need to keep your driver’s license with you. This is just an official document with your info copied to a specific page and then the key to that page is translated into 11 different languages so whomever pulls you over can figure it out.
Sorry, the photos are a little blurry, I took them with my webcam, but you should get the idea; besides they’re official documents I shouldn’t be posting hi-res copies, right?
Do most/all countries recognize it?
There is a list on the application form on click my above like for the mail-in application (I updated the above to say that). It’s a pretty long list.
But I’d think even if they don’t recognize it, a cop might give you an easier time if they can figure out what it means from the additional forms. (maybe?)