[1] http://sanfrancisco.cbslocal.com/2015/03/02/muni-driver-acqu...
[2] http://hoodline.com/2015/10/muni-bus-hits-kills-cyclist-on-m...
The worst in my experience are trucks, and even more so, pedestrians (almost every day I have to pre-emptively break before someone walks into the road without looking)
The average bus and lorry driver always was pretty safe on the roads and courteous with it, of course. They haven't changed.
But there were a lot of idiots out there in all forms of transport who were not so careful and got away with it because "who was going to know?". If it came to an argument it was the cyclist's word against theirs and if it came to court they could threaten to sue for damage to professional reputation if the case was lost by the cyclist. Now with a helmet cam the cyclist has evidence so it isn't just word against word. In most jurisdictions a single helmet cam recording is not sufficient for a prosecution (and may even not be directly admissible as evidence in court) but more than one complaint is usually enough for the bus/lorry company to investigate further (which they will as there are potential fines for not and in some places that threat has teeth) and evidence from official CCTV and on-bus recorders is usually admissible (the former because it is operated by the authorities, the latter because the driver has consented to being recorded). If there is a chance you will get caught and successfully charged with dangerous driving (or the lesser offence of driving without due care and attention) then bad/aggressive/otherwise-unsafe drivers are likely to put more effort into being less bad as it can get them reprimanded by their employer, possibly sacked, possible prosecuted, and it can harm their ability to get driving jobs in future.
So the average carefulness of large vehicle drivers is improving because of monitoring, the perceived average even more so because we never notice the good drivers as much so the bad ones look more statistically relevant than they might actually be.
I have had a "near death incident" or two, so the situation is still far from perfect, but these days I see more complaints about large cars (SUV types and people carriers) and private vans, than buses or lorries.
I completely avoid ever being next to them now, I'll just stop and wait if there's any chance
One time I was stopped at a set of traffic lights waiting for them to turn green. It was on a tight bend and I was about 20cm from the line, and 50cm from the inside of the road. A bus came up and decided for whatever reason he had to get in front of me (even though there was a stop directly on the other side of the junction). There was enough space for a car, but definitely not for a bus as it was on a bend.
He slowly kept creeping forward, and the side of the bus kept getting closer and closer. I starting banging on the window as he got next to me, but no he kept going. I was far enough back that I was out of his blind spot. In the end I had to move onto the pavement.
I then walked to the front and banged on the door, gave him a few choice words and the driver just shrugged.