By the way, I searched on Google and there are some quite in-depth discussions on other forums - I don't want to break the rules by naming any, but one is a very well-known general motoring forum.
The responses appear to be similar to here. A range of opinions, such as:
- I would sand the disc using sandpaper
- I would machine the hell out of the disc to remove all signs of corrosion
- I would grind the lip/ridges but never touch the main braking surface
- I would just buy new discs
and finally my favourite:
- I would sand the disc and then drive around for a week braking quite hard so as to smooth out the scuff marks and hide any trace of the sanding from the MOT tester
One guy said that he had to regularly go in to get his discs skimmed on the manufacturer's warranty.
Have a Google around - there are plenty of people who have had this done on various parts of their brake discs.
Of course, if they are cheap enough, it makes more sense just to replace them, as bugsb said