Just going to chime in here for anyone who googles "scrubbing bubbles on leather" and reads this thread.
I too wondered how well this product would work, so I actually tried it. The leather in my Town Car is made by Connolly, so it is genuine leather, of very good quality.
Obviously, I didn't want to use my car's nice leather as a guinea pig, so I found another Town Car Cartier at the junk yard, and grabbed the leather cover off of it. The car had 205K miles on it, and the leather looked every bit of it:
Usually, when leather is like this, I dilute Woolite 4:1 and go to work. Unfortunately, it didn't do much for the leather itself. Fearing all hope was lost, I ran down to the local Dollar General and grabbed a bottle of Scrubbing Bubbles Bathroom Cleaner.
I simply sprayed it on, waiting ~10 seconds, and gave it a good scrubbing with a nylon bristle brush. (Like you would find in the housecleaning section of any store).
Here's during:
(You'll notice, that nasty black stuff is completely removed. Not sure what it was, but it was a bear to remove.)
The final product (I haven't cleaned the vinyl or "carpeted" areas yet.:
It makes quite a difference. As stated before, due to the nature of the product and the high PH (7+), I would recommend this ONLY on coated leather. If it is uncoated, or suede, it will likely damage it.
In addition, due to the high PH, I would recommend you use it only once. Do a deep clean one time, then regular maintenance shouldn't be a problem. Regular use of this will surely dry out the leather. After use, I would recommend going behind it with a PH balanced leather cleaner, then condition it thoroughly.
I'm going to attempt to "rebuild" this leather using the Leatherique system, repairing the cracks and such, to see how well I can do the task. If I succeed and it looks new, it'll likely go in my car, or be used as a spare for when mine wears out.