How can you use vector blur in Cycles with fluids? I know (at least I believe this to be true) that using cycles motion blur wont work with fluid simulations when rendering, however, I know that vector blurs can be used in place of motion blur.

With that said, however, I seem to be unable to get the vector blur to work in a cycles render of fluid. I have generate vectors enabled as well.

This doesn't seem to make sense to me, since vector blurs are applied after the render in compositing and therefore, in my opinion, shouldn't be affected by the rendering engine.

Any thoughts? Help?
In short:
Cycles (as of Blender 2.67) does not support fluids blur yet.
A GSOC 2013 project might bring that feature soon. 



For now, as a work around, you can try:


Render your primary pass in cycles. Save to EXR.
Render the same scene in Blender Internal, save the Z and Vector pass to another EXR. 
Combine the two set of EXRs with Nodes with a vector blur node. Using the Color input from the Cycles EXR, and use the Z and Vector input from the BI EXR.