All we know that Maya's software renderer does not support rendering of motion blurred particles. These days Mental Ray helps a lot, but because of our bad luck, it does not support passing of data between particleSamplerInfo nodes and fluidShapes. Why that we need a small workaround to get nicely motion blurred particles using Maya's software renderer only.
Create a simple scene with particles, particleSamplerInfo node and a fluidShape colored particles ( through the particleSamplerInfo node ).
Rendering of random frame should look like the image below ( i mean no motion blur ).
The first step for motion blurred particles is ... to create a polySphere. Set the subdivisions to some low values - 10x10 will be enough.
Uncheck all of the Render Stats flags of the polySphere except "Motion Blur" and "Primary Visibility".
Apply a lambert shader and make it fully transparent.
Some people are using background or matte shaders for object culling or other compositing purposes, which is wrong - these shaders are slower than our simple lambert one. Why that, a good idea is to stick with mr.Lambert when you mess with these things :)
Create a particle instancer to snap a polySphere to each particle.
Inside the particleShape's attributes, expand the "Instancer (Geometry Replacement)" frame and set the "Scale" attribute to read the radiusPP data.
Now every instanced polySphere will match the raduis of the related particle.
Activate the rendering of 2D motion blur and set some big values for "Blur by Frame" and "Blur Length" to can easily recognize the motion blur effect.
The same frame but this time with motion blur:
2D motion blurred elements must be rendered in separate pass, otherwise the 2D motion vectors will affect everything behind the motion blurred objects.