Now it's possible to set Dynamic Paint brushes to "smudge" existing paint as they move. By functionality it's very similar to smudge/smear tools found in typical 2D image manipulation programs. This feature is part of my "velocity brush" experiments from last week.
Here is a video of basic smudge:
And now using a particle system as a brush:
Other velocity based new features include possibility to use brush speed to define it's influence and color, and to make canvas velocity or acceleration to affect "drip effect".
Though, I really can't think of any situation where velocity painting would be essential, but hopefully someone will find it useful! :)