The others have summed it up fairly well. The highest I've ever flown and airplane (CRJ series) by hand is FL270, due to the RVSM restriction. I've had the A/P disconnect on me at FL350-380 a few times, and I've left it off for a minute to retrim the airplane. It is just like someone else described as balancing on a pin, and I'll completely agree with KC10FAT about fingertip flying the airplane. It requires a constant nudge here, a nudge there. The CRJ trims itself out very well, but if the flight attendant is in the back with a cart, and she rolls it all the way to the front, I can feel it, and I will have to retrim.
At 31,600 the flight director switches to Half Bank mode, and all turns are made at half what we normally bank at. Airspeed, of course as others have mentioned, is crucial.