Interesting to revive this topic again, storage is always a major issue once you get beyond a couple of boxes of Playmobil.
My neat shelves of 3 Litre "Really Useful Boxes'' from June 2008 survived right up until we started clearing the house in August 2009, though my collection had spilled over into the attic space. Then everything had to come out and go into a storage facility, for which purpose I acquired a number of 84 Litre RUBs, but at 18 GBP each I didn't get enough, and moved onto cheaper plastic boxes, and cardboard boxes. I keep very little in the original boxes, mostly just the very biggest sets and of course unopened stuff.
Sometime in early January we should receive our shipped goods, and then I'll be re-sorting the collection so I can hopefully get at some of it again.
In total (i.e. all my worldly goods) I have 135 boxes and bags labelled and in storage, of which 41 are entirely Playmobil, ranging from 16 of the 84 Litre boxes entirely stuffed with Playmobil, through various cardboard boxes, down to 3-litre boxes which I just sealed with cable ties and labeleld as they were. The total collection I've (under)estimated at a value of 4,000 GBP.
Compared to the 27 boxes of books, or 7 bags of clothes, it becomes clear that if we'd moved about 3 years ago I'd have a lot less to ship!