Many people confuse older styles of circular intersections with modern roundabouts. East coast rotaries, large multi-lane traffic circles (Arc D’Triomphe), and neighborhood traffic circles are not modern roundabouts. If you want to see the difference between a traffic circle, a rotary (UK roundabout) and a modern roundabout (UK continental roundabout), go to http://tinyurl.com/kstate-RAB to see pictures. And here’s another site that shows the difference between an older rotary and a modern roundabout: http://tinyurl.com/bzf7qmg
The FHWA (http://tinyurl.com/fhwaRAB) has a video about modern roundabouts that is mostly accurate (http://www.youtube.com/watch?v=uhHzly_6lWM ).
Modern roundabouts are the safest form of intersection in the world. Visit http://tinyurl.com/iihsRAB for modern roundabout FAQs and safety facts. Modern roundabouts, and the pedestrian refuge islands approaching them, are two of nine proven safety measures identified by the FHWA, http://tinyurl.com/7qvsaem
As to the specific question, it depends. Most modern roundabouts, just like other multi-lane intersections, will have lane use signs posted in advance of the intersection to inform motorists which lane entering can go which direction exiting. The right lane may be a right only lane, a right+thru lane, or a right+thru+left lane. It all depends on the expected traffic volume and which way it is heading.