Actually, Forestry, Railcraft AND Buildcraft use an idea from CovertJaguar (and possibly Sengir) which essentially is "all machines draw power while idle" when using BC conductive pipes. However, the TE energy conduits don't work that way, stopping the power draw.
Ah, I didn't realize that. All of my early-game BC consumers are TE machines and I haven't used BC3 conductive pipes in a while, which may explain why power draw isn't usually an issue. When I'm up to the Therm. Fab. and Rolling Machine stage of my game and haven't yet built up power production, I'll wrench the connection on those machines or simply pick (pickaxe) them up to prevent power loss.
I believe MFR MJ consumers are all loss-less. They seem to be in my experience.