We have showered DS since he was about 4mo (i think!) or once he could hold his head up properly. Our bath is difficult to get to and made my back sore leaning over like that. I just used to take him in with me on my chest and wash him that way usually only about once a week when he was little because it made him so tired.
Now that DS is older he loves playing in the bottom of the shower with his toys and dump truck which we put bubbles in for fun. He plays with the shower head (one of those detachable ones) and loves being able to direct the water flow to his hearts content. We shower each night before bed, but its never usually a full body soap down. Just face, hands, bum and teeth. I do his hair maybe once a week - or two!
(unless he gets food in it or mud or something of course, but he doesnt mind it and knows to turn his face up to let the water run down the back rather than over his face)
I use sebamed baby wash and an organic shampoo. Otherwise just water.
Face and hands get washed during the day, and before meals if they get sticky/grubby.