I took the recommendation on high authority, after a bachelor friend of mine told me that it worked wonders in his shower. Knowing that he's on a quarterly/bi-annual bathroom cleansing schedule, I figured that it had to work.
I sprayed it on and let it sit (thanks to the suggestion) and walked away. I accidentally left it on for like 3 hours, because I got busy doing other things and when I remembered, I did a quick rinse with the shower. It was vaguely cleaner, but not really "great". Disappointed, I grabbed a sponge and wiped over the area and to my surprise it just came off without any scrubbing or provokation. It was slightly awesome.
Then when it rinsed away every shred of evidence that people lived in this bathtub -- let alone an INKER who gets black ink on everything in the whole dang house -- I was impressed. Literally floored.
For these reasons, Kaboom is my new favorite. It was like $3 at Target -- I recommend this to anyone who hates to clean and wants the cleanser to do all the hard work.