Glad it's not just me that thinks this, lane discipline and indication at roundabouts is extremely poor. I particularly hate the ones going straight on when you're turning right, who insist on straight-lining the roundabout even though you're alongside them. Nearly been sideswiped a number of times because of this, and even ended up with my drivers side wheels on the roundabout once!
Also I was taught, and this was backed up by the Highway Code in 1987, that if the roundabout was clear you are free to take the easiest route straight through and ignore lane discipline. I still practice this but my missus thinks it's wrong and prefers to go all-the-way-round using the lane markings......drives me insane.
That's an interesting point, on a normal, "unmarked" roundabout (by which I mean there are either none or very basic lane markings around the circle itself) I'd agree with you, it only really applies to the "straight on" path though, I'd say that left turn is left lane and right turn is right lane pretty much always. Of course if the road is really really quiet you may wish to take a racing line even when turning left or right, but there's no-one watching so that's fine
There are, however, lots of these newer style roundabouts springing up that are very clearly marked with lanes that guide you to the correct entry, passage and exit points. In that case I usually follow the lane markings* even when the road is fairly quiet.
There's a new one way system that has been recently introduced in my hometown, it goes across a bridge, north up one side of the river, across another bridge and south down the other side of the river. It's essentially just a very big roundabout, with a 20mph speed limit. But the locals just simply can't handle it, the join without looking, exit without indicating, use the wrong lane and even drive the wrong way around it. Then these same fukwits rant on Farcebook about how badly planned and dangerous it is. The road is fine, it's the drivers that are dangerous! [/rant]
*of course, the "racing line if the road is completely empty" rule still applies.