My S1 is 10 years old and done 46,000 in the wet and dry (and is garaged naturally). It has some bubbling on the lowest part of the wings under both doors. I was told by a paint shop (that I trust) that it's all down to the aluminium reacting with other metals in that region, (certainly as the only other couple of minor spots on the whole car are by the headlights that sounds right). They also said that once rectified for £800 that they would likely begin to reappear again in 2-3 years time. So it appears to be something you live with, or factor into your 'servicing!'
