"What I set out to do was create a VS designer hosted control that would capture mouse moves on all standard controls and simulate the real tooltip control functionality on the device - and of course it needed to work on the desktop as well. Initially I committed just one day of work on this, but I�m up to four and still counting (lesson 1: never trust developer�s estimates for anything!)."
Marcus Perryman at Microsoft provides a walkthough of his experience of creating a Tooltip control for the .NET Compact Framework and shares the code he used.
I've been wanting tooltips on .NET CF, and was frustrated at the lack of them. I'm quite pleased by the possibility of this, I'll have to play with it when I get home.