the situation at wacken:
people do smoke weed at the festival.
There is no problem with doing so.
There is police around, but not a lot, basically the don't do much against it and if they feel active and do something, i think you only lose your weed if you dont have too much.
if you try to import it:
i come from holland where weed is legal; every dutch car will be stopped and checked on the road to wacken. You can avoid this by taking an alternative route, by going early (they start doing so wednesday or something) or by hiding it well.
From the people i heard that were cought, they also told me they only lost their weed but did not get any other penalty. This probably depends on the amount you have though.
On the festival terrain, about 50 people a day will come and ask me if i sell weed, as they see our dutch cars.......