NOTE: The PlotWatt script in the first post is no longer working. Attached is a working script prototype as of today, based on the work of flaquito.
The reason that the original script does not work is that it only transmits energy values as they change, whereas PlotWatt requires a regular update for the sent values to be valid. This updated script uses a timer instead.
This information is from Zach at PlotWatt:
"It makes sense that the code which is sending data to plotwatt might be doing it wrong. If we don't receive any data points for a period longer than 2 minutes, we consider that missing data. It is up to the client code to report data at every interval it has data for, even if there is no change since we can't otherwise tell the difference between missing data and unchanging usage."
I leave this code to the community to develop as you see fit.
I do no longer use PlotWatt however, since I discovered a better online solution. http://emoncms.org/
is a free open source platform with modern graphics.I posted the emoncms.org integration script in another thread: http://forum.micasaverde.com/index.php/topic,35953.0.html