I read 200 pages of people complaining about this tendency and still complained about it when I got mine
Search for the MM Mod which basically explains how to mechanically trim the swash on a helicopter that flies crooked and auto corrects 99% of the time. It will make rudder inputs a little smoother but at some point you just have to live with it and fly through it.
RoboHeli - My nano dreams were just crushed by the guy working the counter at the local hobby shop. I was ordering a part, mentioned the nano and he said "Nano, you wanna see my 130X?" I may be in love, looks awesome, was ridiculously stable and I had kind of thought of it as too advanced and breakable but he (and 2 other guys in the shop) assured me settings on my dx6i will tame it and it is just about as easy to fix as any other blade microheli. How is your nano treating you?