Driving pattern obviously has a bearing on brake disc condition.

My driving style is brisk, anticipatory and economical (mostly 47+ mpg). I don't need to use the brakes much and so the pads don't wear much. However I only use the car a couple of times a week, so if the brakes are cold and wet when I park up, they have plenty of time to rust.

Every 3 years at MoT time my dealer warns me of the state of the discs, so every 4 years and 30k miles I change them. The outside face is fine because it's well ventilated and it's the inside face that gives the problem. Daihatsu-stu has the right idea in adding ventilation holes and time will tell if that is statically effective.

Probably the best solution is to heat the brakes up a bit prior to parking up when it's wet, so that the discs and pads dry out - but one forgets.

This time I bought discs for about £35 and pads for a good deal less than that. When I stripped the brakes down the pads were only 25% worn so I've re-used them.

My wife recently gave away her 23 year-old rust-free (courtesy of my maintenance efforts) Fiat Uno (51k miles), and the original discs still shone bright. Hmmmm!