Completely finished and updated the example at
http://www.wolfpil.de/v3/coords-in-tooltip.html
When you play around with it, you will notice that the tooltip
sometimes (rarely) looses position. This seems not really
reproducable, only noticable when playing around, zooming in and out,
dragging the map...
This looks like a hardly fixable API bug to me. I noticed that the
returned bounds are randomly junk. Could also be that the conversion
of MapCanvasProjection of the bounds returns randomly junk.