Via this post, I discovered the following video, which basically proves via simulation that roundabouts are far superior to intersections with stoplights. Shown to the right is a bird's eye view of the intersection of Valley View Road (Hwy. 212) and Prairie Center Drive in Eden Prairie, MN. This suburban mega-intersection is the bane of my existence on Tuesday mornings when I have to bring my dog Milo to doggy daycare at Petsmart. Each direction has two left turn lanes, so as soon as the cross-traffic has all red lights, you can't go straight until the left turn lights have run their course...as the picture shows, since the intersection is in hyper-safe Minnesota (which seems to have very long "all red" times in which no traffic moves through the intersection), most of the time the intersection is sparsely filled with cars. If that's not inefficient, I don't know what is. As the video below shows, roundabouts are far more efficient.
Plus roundabouts are fun.