I makeamixture of 1:1 dish soap (does not have to be Dawn) and hot vinegar. Pour it inaspray bottle and spray it on your glass shower doors or surfaces with soap scum. Let it sit for about 20 minutes to so, useanon-abrasive scrubber, gently scrub, then rinse off. The dish soap helps the vinegar to stick to the surface, rather than drying off too quickly while it cuts the soap scum.
Sponges are cheap; you can buy them4foradollar at the dollar store. Just throw them out when they start to stink; no nasty smell on your hands and no fire hazard by microwaving them.