This is true. Perhaps if I counted every time I had to briefly hit the brakes because someone was going to pull out, but then didn't for example, there might be more. But in 7 years I've had a mere handful of times when the incident was such that I might have felt the urge to shout profanities and wave my arms around a bit.It depends on what you class as an incident really. I consider myself a competent and reasonable cyclist, but in the year I've been properly road cycling I'd say I've had 3 noteworthy incidents. Small incidents that I don't remember on an iduvidual basis? Many many many more, these probably occur about once or twice every three rides, as a rough estimate.
That said, I find the majority of drivers at least attempt to drive well; most are 'average', many are 'satestfactory' and then there are the ones who are good or great, even those are more common than the bad drivers, in my experience.
In fact, the number of truly, truly bad drivers I encounter these days is easily exceeded now by the number of cyclists that I see doing reckless things (I'm not talking red light and pavement stuff here - I'm talking about filtering through rapidly closing 2 foot gaps between buses, and pulling straight out of side turnings into the path of lorries expecting everyone to stop for them etc). Of course that might not be the same London-wide, but it's what I observe on my route anyhow.