I decided to try some Mobil 1 synthetic ATF in my Rohloff after reading here about another user's success using it. Well, I'm not "thousands of miles later", but two months into it (about 800 miles) I would say that I'm pretty happy. It's not an exponential change, but I would estimate that it's about 5% smoother (if you can even gauge that). I've also noticed less missed shifts / freewheeling.

I didn't really know what to use for the whole initial "cleaning" process, so I just rinsed the hub with the ATF twice. I felt like I could have cleaned it probably 2 more times as well!