[wirrbel]

A local theme park as a "dutch quarter" and I as a kid was always fascinated by one booth having a letter "ÿ" in the name. I later learned that it was some kind of alternativ spelling for ij, and if you spell ij in black letters its really easy to see why that might have occured.

[thequux]

It's also quite common in handwriting; ij in cursive looks exactly like ÿ, and even when the letters aren't all joined, that is a common ligature. When I studied Flemish as part of the integration course, all of the teachers wrote ÿ, and so I presumed that it was just the done thing.