here's a quote from Coders at Work's Dan Ingalls interview that made me sad:
Seibel: What made the Smalltalk debugger so nice?
Ingalls: Well you could stop anywhere in the program and you could actually look at all the bindings of all the variables. You could execute fragments, evaluate expressions right in the middle of the context.
Seibel: At any particular point in the stack frame?
Ingalls: Yep, and you could make significant changes and then proceed. And you could get to an error, have it on the screen, save the entire state of the system, ship it to somebody else who was on a Windows machine and not a Mac, and they could fire up the same image, be where you were, make a fix and proceed. So just complete preservation of state across different machine representations.
Jason Forrest
Amy Hoy