March 30, 2013 Update:
Puttronome Application update on the iPhone today. Really nice update and improvement. Stays running, has a light sequence to help you to start, and a tempo window. Very cool!
This video demonstrates putting tempo. I first learned of it during my Harold Swash Putting Level 1 instructor course. I have it on my iPhone, and use it daily as a warmup putting drill; full swing too!