In the UK its priority to the right, meaning if there's something coming around the roundabout, you must/should wait... Which only works of there is a gap in the flow of traffic big enough for you to jump into...
Don't worry USA, you'll soon regret your decision to introduce roundabouts.
Stick with your sensible "right on red" logic, and your sweeping circular on/off ramps (yeah, you and Canada have plenty of space to do those) - they are genius for maintaining traffic flow (not so convinced about the traffic lights leading onto the freeway though at rush hour times!)
If you fancy a giggle of what mayhem roundabouts can cause, try searching for "spaghetti junction" near Birmingham England, or "the magic roundabout" of Swindon England fame - they are priceless!
Enjoy! ;-)