Like I said before it's good to see some actual competition in this space.
I find it interesting that it seems that for a some people, Blender is their first experience with a node-based editor. They've been around for years. While I haven't used Nuke (or Shake), I was very good with Houdini for CG which is all based around nodes. It does include some basic compositing (or at least it did the last time I used it).
The other big node-based thing is audio synthesis / effects, for example Pure Data. As far as I know these are the only areas where dataflow programming has really taken off.
Matlab's Simulink is also node-based (probably because of LabView). It's also widely used.