I gave builder a try again yesterday while doing some GDM hacking and for the most part it was a drop in replacement for vim for me.  The main hangup I ran into is split screen handling (which I use a lot when navigating, or cribbing off code).  In vim, I use:
 
ctrl-w v to start vertical split views
ctrl-w w to switch between views
ctrl-w c to close a view

in builder ctrl-w closes the current document.  I think in time I could train myself to use the current gnome-builder keybindings, but yesterday I just kept closing my buffer and finally gave up and went back to vim for a while.

Would it make sense to match the vim keybindings?