Shame pump manufacturers don't put a power usage/head graph on the box, like they do with flow/head.
I have one of these:
http://www.walruspump.com/documentation/pw100.htm

Rated at 100W - but turned out to be 240W+ at 1M head.

The power usage should decrease with increasing head.. I think.
I might be wrong here, but I THINK this might be right....

There is more load on the motor, so flow decreases, power increases.
Even my little 32W power head was actually 38W with significantly reduced flow at 1M.
It takes 147 watts to constantly move 1 litre of water 1m vertically in 1 second, assuming no electrical losses.
Hook up a DC motor to an ammeter, let it run freely, then add some friction, amps++

With regards to head, aside from actual vertical lift, diameter and length of pipe must also be considered. I know this from years of research into saltwater aquariums (something I still haven't had the balls to commit to...one day...). As much as one might think, "Sweet, 8000lph at 4m head, well I'm only pumping 1m to my tank", if the pipe is only 20mm, this may create enough back pressure for the pump to actually see 3m of head and therefore draw more power (numbers pulled from the air for argument sake).

Yea Dui is correct, more head - more power is needed.

Absolutely correct and 90 degree bends (or in fact any angle bends) also effect pump load and therefore power usage and flow.

I finally got my power usage meter on ebay.
So contrary to what is intuitive and also agreeing to points on another thread somewhere..
A pump will use LESS power for the following reasons
1. Bigger head
2. MORE restriction
3. Anything that REDUCES the water flow.

It seems counter intuitive but the principle is the same as when you put your hand over a vacuum cleaner. What happens is that when you restrict the flow the pump actually has LESS work to do and therefore uses less power. When you put your hand over the vacuum cleaner the moter revs up, or spins FASTER. Why? Because it has less load, and less load means it can spin faster.

I have evidence as well, only in verbal form.
My old 200W ebay pump:
-running with only a short length of hose (max water flow) 135W
-Pumping up to my GB through lots of little holes 100W
-My finger jammed in the pipe so ZERO flow 85W

New Jabao eco pump (awesome pump)
-running with just included fittings (full flow) 48.5W
-running with my finger jammed in the end (ZERO flow) 44W

of course for the SAME FLOW RATE at a higher head you will need more power, thats obvious. But that is not using the same pump, you just need a bigger more power hungry pump.
With the same pump at a higher head, your flow rate decreases (of course) and the power consumption also decreases (not so obvious)

QED

Interesting.
The above is definitely not true for a DC motor.
I thought I might be going insane, so I just tried it on the bench.
630mW unloaded, 987mW gently loaded, completely stopped it blew the fuse in the DVM

So Watt's (oh no, can't believe I just said that) different with a mains AC motor?
We should probably take this out of Ghengis' Thread, sorry for the hi-jack !

You're right in that when you load the motor it draws more current.
What I am saying is that reducing the flow rate of the pump by adding head etc reduces the load on the motor not increases it..
So try it with a DC pump
Yes sorry for the hijack