I've done some more research into this issue and it seems to start happening once you get a certain number of cable length away from a power source. You won't see it usually with just a couple machines hooked directly or nearly directly up to a power source.
The attached screenshot shows a setup that works with no spam, but if I add a single induction furnace to either end, I start getting spam for that furnace. Add all four and that's 4 spams multiple times a second. For reference, the power source is one of APM's Adjustable Emitters set to 32 eu packet size and 2048 eu/t output. Plenty of power going into the system, just not being used correctly.
This looks like possibly a combination of EnergyNet and machines not working properly and it really needs a fix. The sucky thing is, the machines DO get powered, they are just spamming up the client/server console and lagging the hell outta the game.
--edit--
Looks like Player fixed it for the next release.
http://bt.industrial-craft.net/view.php?id=213#c584
Confirmed, tried the latest build (184) and the spam is gone, energy net is working correctly.
http://ic2api.player.to:8080/job/IC2_lf/184/