The leather is really easy to clean. The leather in the car has a coating on it. That coating protects the leather. It's not like uncoated leather which becomes dry and needs to be rejuvenated with oils. So with coated leather you are cleaning the actual coating and not the actual leather. If the coating has failed, one will see color transfer on the applicator.
I pulled this from a thread on Autopia car care.
Caring for pigmented leather is truly about keeping the leather clean. Dirt and particulate will scratch and wear the leather leading to shiny appearance and exposure of the leather hide underneath. Acidic body oils can wear or stain the vacuum frequently and use a gentle, water based cleaner to remove embedded dirt and oil. Use a protectant or conditioner that features protectants (to reduce abrasion and increase sun fade resistance). Over time the leather coating will crack microscopically or stretch in the seams and folds. Conditioners can penetrate the coating through these cracks and openings, keeping the leather underneath soft and supple.
This is a good reference video
In regards to products, some All Purpose Cleaner would work on all surfaces. I would recommend something like Meguiar's D101 with the spray bottle mixed at 10:1. It can be used on most surfaces. I have used it on leather and the plastic interior pieces with no issues. It can be used on upholstery as well. I would recommend getting a brush to scrub the leather seats to pull out a lot of the dirt. I have used APC on leather but it can sometimes leave the leather feeling a little sticky. So following up with a damp microfiber towel can help with that. I personally follow up with a leather conditioner to add a barrier between the seat and the person. I use APC for deep cleanings.
If you are looking to pick up some products locally, Meguiar's Gold Class Leather & Vinyl Cleaner and Meguiar's Gold Class Leather Conditioner work very well. These are strictly leather products.
Meguiar's Quick Interior Detailer has a light cleaner built in that can be used on all surfaces. I use a lot of this and would recommend it. For a heavily soiled interior, APC is the way to go.
Here are a couple reviews of some leather cleaner and conditioners that I have done.
These Blackfire products are great and would recommend them as well.
http://www.autopia.org/forums/detail...nditioner.html
These Meguiar's products are only available in gallon sizes.
http://www.autopia.org/forums/detail...r-cleaner.html