Not lived there, but visit for work.
Cost of living? Not as cheap as it used to be. It’s pretty much on a par with any other major world city these days. Some superb food, though!
Accommodation – Not too sure, to be honest. However, I usually stay with a mate who earns a ” pretty reasonable” wage for a mid-30s professional, and he has a nice, but small, two bedroom place ten minutes walk from Bondi.
Quality of life? Ace. Lovely, slow lifestyle. Like stepping back in time sometimes! Beaches, nice weather (much of the time) and a very nice relaxed culture (At least around the CBD). Weekends still seem to be weekends, not just another day to check your Blackberry, which is really refreshing.
Friendliness of the locals – Overall, great! However, outside Sydney it gets much, much friendlier IMHO. As with any major world city, I suppose.
One other thing – Sydney is HUGE! Sprawls for miles and miles, far beyond the size you might expect for the population.