From the same thread, it seems the problem was caused by BusyCal’s “animate transitions” preference. I didn’t try that, but if you are still using BusyCal 1.6 and have this problem, it’s worth trying.
How to stop com.apple.dock.extra from "using significant energy"
I’d been having for some time a problem with `com.apple.dock.extra` appearing in the “Apps using significant energy” section of the battery menu. I just learned the solution (from http://forums.macrumors.com/showthread.php?t=1651662): remove BusyCal 1.6 (I upgraded to BusyCal 2, but left the old version around in case I had to go back to it). After removing it and restarting the Dock, the problem stopped.