It's actually a godsend to people who, like me, need to get around the perimeter of London, rather than crossing it. I use it a lot, and yes, it carries a huge volume of traffic so yes, at times you slow to a crawl, or sometimes stop altogether.
Without the M25 London would simply not work, however, so despite it's shortcomings it is exactly what I said - a godsend.
To return to the key point, or what I think is the key point of the thread, you aren't automatically a menace just because you don't use the motorway regularly. As long as you know both what is supposed to happen and have some sense of what actually happens.
"As long as you know both what is supposed to happen and have some sense of what actually happens."
Good advice, and something that someone should tell my satnav system. It thinks that the M25 is the road to everywhere, so it tries to route me onto it at every opportunity. Years of driving in and around London have provided me with a personal database of short-cuts and (relatively) traffic-free work-arounds however, and at times it is very irritating to be told to 'turn around, as you are going in the wrong direction'.