I've added a lot of highway=turning_circle (originally this said traffic_circle, oops),source=Yahoo tags with Potlatch. The r (repeat) key is a real timesaver here (except there seems to be a bug where sometimes every tag from a node is repeated, not good if it has TIGER data).

That said, I just realized there was a better way to do this with JOSM. Shift-select all of the turning circles, and add the tag just once.

Now if only the JOSM imagery was as good as Potlatch....