Well I was cleaning 2 of my spare alloys on Sunday (no CC at the moment so nothing better to do). I noticed that the reverse side of the wheels were badly pitted and the alloy surface had come away.
I looked at Melanies car which I had treated from day one with the Instant Tyre Dressing and hers were fine (mine hadnt been treated).
Either keep an eye on your wheels or treat them with some sort of protector.
Looks like it may be a warranty claim as wheels shouldnt go like that with less than 10,000 miles on them.