I don't have a washing machine at the moment so sometimes I do undies, socks and shirts by hand if I don't feel like trekking to the laundromat. Hubby was critical of the idea at first - "will they get clean enough?" but once he saw the results he shut up. I don't think washing machines get clothes particularly clean, especially the front loading ones that are all about using less water - you need a certain amount of water to rinse the dirt and the soap out. Although most people wash clothes that aren't really dirty anyway, so it doesn't matter much.
I agree with Moolie - forcing the water through the fabric, not scrubbing, is the key.