A friend told me that one of the best ways to cut the soap scum to almost nothing is to quit using bar soap and start using a liquid body wash. The chemical composition is completely different, and apparently it doesn't form the scum.
Yeah, all that build up is talc or whatever they put in to make bar soap stay in bar form.
Liquid soap gets rid of lotsa clean up problems.
The BEST thing is soft water.
For removing lime buildup, soak a small towel in cheap vinegar and leave it on the buildup for a good while.
Car wax on shower stalls, spas whatever works great. You can even use it on the stall floor if you also use a good shower mat.
Also, the suggestions of pumice stone are great because the only other option is high explosives.
So, what a lazy man needs to do is:
soft water
liquid soap
whatever left over car wax is in your garage
a quick towel wipe down in the shower after use
You'll soon find shower cleanup to be just an every now and then chore, almost a thing of the past.