Well, for myself, I researched the heck out of this topic over on the autopia forums in order to try and restore the steering wheel on my newly purchased '09 M3 with a sticky/tacky and shiny steering wheel.
I used a combination of steam towel, soapy warm water and a toothbrush with MANY passes, which worked wonders. Then followed it up with Leather Master Foam cleaner (foam version of their "Strong Cleaner"). The results have been great, but there is still a bit of a "sticky" feel after my hands have been on the wheel for a bit...I'm thinking some of the urethane coating has come off...? But I'm not getting color transfer, so who knows...may just need a few more passes.
I'm going to put some Leather Master protection cream on and see if that helps.
But all in all, I can say you can get great success with warm soapy water, a toothbrush, and patience, and the Leather Master stuff is great as well!
I think we all forget that our leather is coated, and most of these leather conditioners on the market are just putting oils onto the coating, which is not the ideal solution. We need water-based cleaners and even "conditioners" (LM Protection Cream is supposed to be great).