Or cyclists that go down a road at 20 when there is a specially built cycle path just for them going alongside the road!
If you had ever tried to cycle down a cycle path at 20 mph then you'd know that the road is a better choice. It is recommended (by a QUANGO), with good reason, that if you are a cyclist travelling quickly, to not use cycle paths. A source for that claim escapes me currently, but I will find one.
Yep. And those who have almost no ability to ride in a straight line, swerving in and out from the curb constantly.
Generally they'll be avoiding potholes, grids etc. As you get more experienced at cycling on the road you'll plan ahead better and look behind sooner to make your intentions clear. It's often necessary to move out into the road to avoid potholes, which would you rather; a cyclist breaking a wheel, coming off and lying in the road, or a cyclist moving a foot to avoid a pothole?
My main gripe is their road position, mainly at lights and junctions, or in general really.
I don't know what you mean by position at junctions, but in general it is much safer for a cyclist to be 1m from the left hand curb than <1m for many reasons. There are fewer potholes here, so the cyclist isn't having to change his or her road position, so they are easier to overtake. Them being further out makes drivers unable to squeeze past when cars are coming the other way, so it is safer for the cyclist. Cars will generally give more room when overtaking when you are further out. If a problem arises, there is room for the cyclist to move to either side of them.
Following on from that subject is this:
http://www.timesonline.co.uk/tol/news/uk/article6828100.ece
Which most cyclists will have noticed as soon as they used a cycle path which is part of a road. I certainly always cycle along the line at the edge of such paths.