Matt
Just made a correction, it July 2010, not 2009 ... its an age thing!!
We were told that whilst overnight "camping" is not permitted in general, overnight "parking" can be tolerated. This was from a Portuguese camper in Portugal and a apparently person of some official standing. This seems to apply to both Spain and Portugal. The camping distinction is do not erect awnings or put out tables/chairs etc. We generally chose camp-sites as they were reasonably priced and as it was quite hot our fridge benefited from a night of mains power and its good to have showers at the end of a drive. So its not quite as official acceptance as are the Aires and may depend on whether the official can be bothered. We always chose an unobtrusive location but not too remote and usually with some other van nearby.
Another aspect we were told for Spain, at least,was that its allowed to use toilets in bars and cafes etc as the Govt helps fund these instead of building public loos.
jon
1.9 DG WBX, 5 speed gearbox, standard steel wheels