Great work!

If you want the ability to change the hover text, you'd need to figure out how to do the "update" function to just change the text in the hover div.  Knockout will automagically call "update" when the valueAccessor observable changes (if it's an observable).

I believe you can sneak your own observables into the binding context (like the popup div), if you wanted.

In any case, glad to see cool stuff like this!  Great having more people on the team :)