A British friend has given me a copy of the British Highway Code as it pertains to roundabouts.
One of the big differences between a roundabout and traffic lights is that you never have to wait for non-existent traffic. If the roundabout is empty, you can go. Another difference (at least until you get used to it) is that if the roundabout is full, you can be stuck forever waiting to get onto it.
To a foreigner, like me, signalling was very confusing at first, but after riding with a few British friends, I think I understand the tricks. If you are going off at the first left, you stay in the outer lane and signal a left turn. If you are going straight through, you don't indicate. If you are going off to the right (three-quarters of the way around), you use the inner lane and signal a right turn. The last one confused me at first, since initially you signal a right turn and move to the left.
One of the stranger advantages of roundabouts is that you can never get completely lost. If you find yourself driving the wrong way down a street, all you have to do is get to the next roundabout, and turn 180 degrees. This is a lot safer than doing a u-turn on a busy street, since the other motorists will already be expecting you to turn.
On the other hand, roundabouts are subject to the same gridlock that we get in North America, but with roundabouts, the gridlock is pretty much guaranteed to lock up all the nearby streets, because the traffic jam will extend right across the roundabout. In North America, if everybody drives legally, gridlock should not block the side streets, because nobody is supposed to stay in the intersection.
Or this could happen when you get a lorry (truck) which decides to stop on the roundabout. Before you say that would never happen, let me assure you, it does! I was in a line of cars waiting to get onto the roundabout, and the driver of a large lorry stopped on the roundabout, got out of his cab, and walked to the lorry behind him to ask directions. What made this a disaster was the fact that his stopping held up another three lorries, which were then occupying the entire roundabout. All us other drivers had no choice but to wait until the lorries moved.