Fill up an empty spray bottle with vinegar. Don't dilute! Spray down your tub/shower and wait a few minutes so it has time to work it's magic. Meanwhile, go find a good and sturdy scrub brush or two and a box of baking soda. Probably should wear a mask too... the vinegar is a bit potent.
Rinse everything down when you think you've got it all done. Realize you don't. Repeat process.
Cleaning my entire tub/shower unit took me almost an hour and a half. So this is not a super quick 5 minute process. I am super excited this worked though! I was getting to the point that I was considering purchasing a whole new unit because I was afraid to take a bath. Plus I didn't want to put my future babes in a dirty tub. A $3.78 baking soda/vinegar fix trumps a $500+ purchase any day!
I also had another Pinterest epiphany and am hoping this will prevent me from frequent heaving duty scrubbings. Fill one of those dish scrubber things that hold soap in the handle with a 50/50 mixture of distilled white vinegar and Dawn dish soap. I hung mine off my shower caddy and supposedly if you use it to give your shower a lick and a promise every few times you're in there, you won't need to do anymore/as many heavy duty cleanings.
Go forth, be clean.