Just to support arnie really; hot soapy water is powerfull enough, yet kind and gets suprising results.
I use the soapy water on the door cards and under dash area to keep things clean.
After using soapy water, treat the leather with a 'food' (not cleaner) to restore suppleness and replenish lost oils.
I do a lot of detailing, but have had some disasters with leather and the dye coming out. From this day forward, if soapy water doesn't cut the mustard, I would take leather to a pro - so if they mess it up, its their problem.