all these cliches people are posting here are just extreme saftey measures, that are useless in real life. and "working over 2m should be footed any higher secured with lines from the strings of the ladder staked into the ground", well thats just rediculous......
if i go up to a window, then if the ladder was up 20 feet i'd say i usually have it about 10 foot from the wall. i do that every day of my life and i haven't had a ladder go back on me yet and i have spikes. it is true that you roughly need to put your weight above a ladder. but that said, its unlikely that a ladder would slip even if you put it up at 45 degrees. infact, i used to work with a lad who pitched his ladder up at even more than that!