I thought half an acre was bad... But then again, mine consists of plenty of trees with their roots above the blade line, so I gotta be extra careful. And then there's the back yard, which includes a steep 45-ish degree hill in which even the riding mower can't tackle well. We've got a rear-engine Craftsman mower and it got stuck on the way up the hill. Twice. Guess the rain was worse than I thought. Nothing's more fun than having to hop off and slowly lower it down the hill while holding the brake pedal with your hand.

All in all though, my lawn takes about an hour and a half, give or take conditions.