I'm looking to change the behaviour of the silverlight maptip. I want the maptip to stay up until a button on the maptip is clicked. I figure I can make the maptiphidedelay really large to keep the map tip up but how can I overwrite the mouseleave method? Can a button click even interact with the visibility of the maptip?
Correct. This is not the behavior of the maptip.
You can also use the MouseLeftButtonDown event on the graphic to pop up a UserControl on top of the map. Use the screencoordinate in the mouse event to determine where to put the usercontrol.
Light weight marker + one usercontrol will be way more efficient. If you have a lot of data you always want to keep your symbol templates as simple as possible.
Note: I wouldn't generate a new usercontrol instance on each mouse over. I would just have one present on top of the map, and toggle the visibility and move it to the location of the new marker on mouse enter. Set the DataContext of the control to the graphic to update the contents in the custom maptip, just like "normal' maptip works.