Parking and tight manouvering only.
Last month a friend in his Renault 5 (don't laugh, he's surprised us all and got a car!) had to get out a tight space and he has no power steering. Well, back and forward, back and forward etc, and I bet his arms were tired before he'd gone anywhere.
Before my Punto I had an Astra without power steering, and so initally the city mode was so light! Now my arms are used to the power assistance (and therefore weaker), city mode is usable and useful. But I'd never use it out on the open road...
Punto Mk2 ELX 8v in Teseo Blue with the electric Sunroof and CD changer, doing 50mpg whilst passing down country lanes