You'll probably find ghosting (rusty outlines)on the disc surface where the pads were stuck. The insides of the discs tend to be worse then the outsides. A few applications "from speed" should help, but once marked it will never go completely.
A painful lesson I also learned a few years ago... I washed my M3 Evo and put it away in the garage for a couple of weeks. The front disc pads rusted solid onto the floating discs. I had to slip the clutch
hard to free them with a large bang. This left pad marks and surface rust on the discs which I tried to remove with steel wool (Brillo pads) and fine wet and dry wrapped around a mild steel block. Despite this and several heavy application attempts to clean them it wasn't possible (as Dave W says above the marks remained) and the juddering remained. The only solution was to replace the discs and pads
Ever since, every time I wash my car I run it round the block and preferably left foot brake (note some new fly by wire throttle/engine management systems won't allow this) or failing this give them several hard applications until the brakes are dry and hot before putting the car away. Interestingly, the new BMW handbooks now advise this
Neil, I hope your discs clean up... good luck!
