Mmmmm...... just read this thread while playing catch-up with the forums.
Just a couple of observations here:
Firstly, my only 'fault' accident in over 40 years of driving (the other two were being 'rear ended' when stationary or very nearly so) actually may have some relevance to the whole speed cam argument.
It happened in Weymouth a good number of years ago whilst on holiday there. I was travelling into Weymouth toward Portland Bill. As I recall, there was a bridge crossing a river and the traffic was fairly thick and travelling at maybe 20-25 mph. It was raining fairly heavily. I was in this stream of traffic and (mainly as a result of being rear-ended a coupl of times) I was a bit paranoid about the rear view mirror, constantly checking it. I was aware of a car following fairly closely and, yet again, checked the mirror. On returning my eyes to the road, I noticed that the vehicle in front had its brake lights on so I covered the pedal. By the time I realised that it was in the process of 'full-on' braking, it was too late. I slid gracefully into its rear bumper at about 4 mph!
Now, had I seen it start to brake, I'd probably have realised that it was braking hard by noting the attitude of the vehicle. So, I conclude that by missing that vital split second's worth of information (by looking in the mirror) I missed the 'cue' that I needed to 'stand on them'.
I see this as analogous to the situation created by the obsession with speed whereby constant attention to the speedometer is required. That split second could lead to the loss of that vital split second's worth of information that makes the difference.
Still with me??

OK, on to the second point (who said "Get on with it!"?)
Bends with advisory limits: I agree that most seem to be set awfully low, however, there is one near where I live (it's on the Acle straight - part of the A47 leading into Great Yarmouth if interested) which is marked 40 mph. Probably not because of the bend per se, however there is a junction on the apex and a pub (Pontiac Roadhouse) opposite. Now to me, that appears perfectly logical, and, taking account of the conditions, traffic etc, it is safe to take the bend at the limit current (NSL - single carriageway, 60 mph). However, I've lost track of the number of times I've encountered people who promptly drop to 40 mph and stay there for the next 7 miles of dead straight road all the way to Yarmouth. They are apparently seeing this as a limit sign, and, in conjunction with all the camera warning signs, believe they are in a 40 zone and stick to it.
Supplementary point: I've also met a huge number of people who travel on similar roads at an exact 50. I can only assume that they are not exactly up to date on limits.
Just an observation (or two). Cheers, Chris B.