my heater during winter is 2000W, and my aircon during the summer is 1600W, my main pc draws nearly 500W, my dryer is something ridiculous like 2100W, normal appliances can stack up substantially more than a hydro light
companies can't monitor your daily usage either (to see your 18/6 or 12/12 pattern), if they could they wouldnt send people around to read the meters, and meter-readers cost them an awful lot in labour...
if you were to deck out a house with 4 1000's in every room, then you might have issues, and it'd be more from the leaking of light, the noise of the exhaust fans, from normal people that have eyes & noses, like postmen, pizza delivery guys, avon catalogue people, etc
and just for the record, 2x600W lights might give you theoretically 30,000odd more lumens than a single 1000W, but the overhead with old ballasts can blow the power usage out
for instance, my 600W lights draw an average of 720W each, whereas my 1000W draws just over 1100W, this equates to a bit of a saving over time, a single 1000W will also put out less heat, and get better penetration (not coverage) than the pair of 600's.
regards