I have thought about roundabouts for a bit. After this, I have come to the conclusion that they only work in situations where there are four or more possible turns, but the vast majority of traffic is heavy on just one turn.
There's no good light cycle to deal with this situation. In this case, a roundabout does speed up traffic, because there's little competition for space in it, and the odd car coming out of the rarely used parts of the intersection won't have to wait fifteen minutes for their part of the cycle.
Another good place for a roundabout is one where a left turn is impossible with stoplights, because the angle is too sharp. Putting a roundabout there enables the left turn, since you're really just making three right turns to do it. The Dunn/Hillsborough intersection is a perfect example of this, and there will be a roundabout there. I'm content with that.
However, I don't want us to get into the habit of putting roundabouts on intersections just for the heck of it. Hillsborough is an important street for getting into downtown Raleigh, and crowding it with too many roundabouts to slow traffic to a crawl would probably hurt business downtown (and on Hillsborough) more than help.