Well, I just cleaned my boat today, and found out that I didn't have any Lime-Away, and then I remembered someone talking about toilet bowl cleaner. So my wife had some toilet bowl cleaner called "The Works". My outboard is black and so is my hull. So I wet my outboard with a hose, put some of the cleaner on a wet sponge, and did a small spot on the outboard. Washed it down, dried it and wow it looked just like it did when I bought it. I then did the entire motor, my entire black hull, and it looks beautiful. You can easily see spots you missed as soon as you wipe it dry. Re-apply in that area, rinse, wipe and finished. Man for 6 years I would get under the hull and painstakingly, try to get the white grime off of my boat. Somebody shoot me for not asking sooner, Ugh. Anyway, it took all of about 30 minutes to do the entire outboard and my entire hull. Man I feel like I won the lottery.
Anyway, I'm sure other toilet bowl cleaners would work as well, as I know Lime-Away does also, because I just spoke to one of my club members and he uses it. So I thought I'd post this as another product that works really well.
Note: Wear eye protection and some rubber gloves, as the toilet bowl cleaner is acidic.
Thanks to everyone for all their input.