There is new tool for bi-directional constraining which looks quite interesting. Each node has constraint "blue channel" input and apparently Maya doesn`t make pairBlend node when you make a keyframe on its transform. The keyframed motion of the object is probably enabled by the bi-directional node as well which handles the keyframe inputs.
So the first look seems like a good implementation in Maya animation system.
There is currently a beta testing open to those interested. For more info go to the Exotools webpage:
Supported Maya versions are 2009, 2010 and 2011. Plus OS: Windows, Linux and Mac