I saw a few 70mph limits in Southern california last week...
In England, the A-roads (typically two lanes in each direction separated by metal or wire crashbarriers with a safety "hard shoulder" lane on the outside) and Motorways (same thing but typically with more lanes each way and no right of access to slow moving things) the limits are in each case 70mph for cars.
The UK's 70mph limit was established in the late 1960's and hasn't budged since, despite engineering advances for everything concerned (roads, vehicles, drivers...). It was principally brought in because companies like Jaguar were routinely testing prototypes at 150mph on the public road, which I guess isn't the smartest thing in the world.
Most people (ie >80% of the cars here) travel at about 80 to 90mph on motorways. Of course everyone slows down to go past speed cameras and police cars. Truckers in the UK have a meter which is sealed inside the cab by an inspector and that limits them to exactly 60mph, which is what all trucks in the UK do pretty much no matter what the real speed limit is (ie. if the road says 50mph limit, they'll normally be doing 60).
If you get caught speeding there's a range of things that can happen. The typical 10 or 15mph over the 70 is a fining matter (the fixed penalty for this type of offence is £60, which is about US$100) plus 3 points (you start out with 0 and can have up to 11 points without losing your license). Conversely, 10 or 15 mph over a 30mph limit would likely result in a ban. Points cost money because the insurance companies are privy to them and they will see you as a bigger risk and raise the cost of your policy so in effect you get fined for the next 5 yeasr by your insurer on top of the on-the-spot fine.
Dangerous driving carries higher penalties (and is recognised differently in the law); in the result of injury to another person caused by recklessness you can of course go to jail, etc etc etc. This also applies where extreme speed has been recorded (over 100mph).
For a typical speeder, if you go over 100mph, you ought to expect to lose your license. I think the record on a public road in the UK is about 156mph (http://newswww.bbc.net.uk/2/hi/uk_ne...nd/2973149.stm
) - ironically this guy shares my surname (I'm pretty sure we're not closely related though!).
I know that some people have gone faster - for example a couple of car journalists have said things about maxing ferraris and lambos on the public road (so we're talking 190mph).
Fastest I've ever been in a car on a public road?
About 160mph in Belgium, in a 911. I was a passenger.
Fastest passenger ride in the UK was probably about 140mph in an M5 but I couldn't see the speedo at the time, just the little digital readout on the radio.
Fastest I've ever driven?
I'm not saying where, when or what I was driving but it was at night and I did about 125-130 with no-one around. I'll not be doing it again now that I've satisfied my curiosity!
I did much the same speed on a circuit in a noble M12 GTO and I must say the noble felt much better at that speed.