it is possible to define additional classes and functions inside a VB component (look below the main function, there's room there for additional type declarations). However you cannot share those classes with other VB nodes since they are not aware of each other.
Do you think complex numbers are useful enough to add to the standard toolset of Grasshopper?
just came across this topic, and me and another few guys (Alex and Irina) think that it would be great to have them. Thinking about other useful things, it would be nice to be able to simply create "buttons" with parts of your own deffinitions (which you are using often let s say, like the shelves in maya)
Yet if you defined a class outside of grasshopper I think you could reference it by multiple components if you did want to use a class in multiple places.