I have personally driven with various U.S. state licenses in the UK, France, Germany, Austria, Switzerland, Liechtenstein, Jordan, Israel, Canada, and Argentina. In the vast majority of countries worldwide, licenses are valid on a reciprocal basis for the first X number of days/months you're there, where X is a period of time far greater than your average business, vacation, or VFR trip.

The International Driving Permit (IDP) is NOT a license at all. It is simply a translation of your license, indicating who issued your license and what type of vehicle you're licensed to drive. It is useful (for Anglophones, anyhow), in countries where English isn't widely spoken. For example, if you're stopped by traffic police in Argentina, it says in Spanish that you're licensed to drive the vehicle you're driving, theoretically eliminating all kinds of hassle.

This works out just fine in most cases because the "rules of the road" are more-or-less universal, the major exception being left vs. right side of the road, which is simply a case of mirror-imaging everything you know about driving - not that hard when you actually do it. Of course, the rules of the road are observed/enforced with varying degrees of strictness around the world, ranging from very strict adherence in Germany to more lax attitudes in the developing world (places like, in my experience, Jordan and New Jersey). To me, driving in a new country is part of the experience of getting to know the place, and I will go out of my geographical and financial way to do it if possible.

The major learning curve for most foreign drivers (whatever "foreign" might mean for you) is signage. Most of the world uses a standard system that's heavily dependent on symbols and drawings, thus not requiring the driver to know much of the local language. The US and Canada are among the very few places where a different system is used, more dependent on written words in English/French. Beyond that, it's incumbent upon a visiting driver to learn the few other peculiarites of driving in Country A - default speed limits, parking regulations, what to do if a collision occurs, and so forth. This information is available for most countries by doing a simple Google search.

Cheers!