You get most of the same functionality by saving off Smalltalk images with meaningfully arranged windows. (Yes you can do it with debug sessions too.) But you have to keep track of the relationships yourself. The lines and groupings are genius.
This stuff is awesome. First time I've been this impressed by an IDE outside of Smalltalk, Self, or Symbolics, Lisp.
I also appreciated the fact that it linked called functions to their definition. g] is great in Vim, but it is easy to get a little lost in the navigation stack. Having g] intelligently pop out a new buffer window ala :vsplit would be a great start.
They have some great grouping features - snapping, colouring, pushing, connections with lines, naming groups.