To get data out of the Concept2 PM3/4/5 easily I use a script called PyRow created in January 2012 by Sam Gambrell. 


"PyRow is python code that allows one to interact with a Concept 2 Rowing Ergometer PM3 or PM4 monitor using built in functions or csafe commands" - Sam Gambrell


UPDATE Feb 2015:

PyRow has been updated and the documentation improved by UVD, and is now available via GitHub: