My Realflight G2 was always able to work flawlessly in Boot Camp, but now it also works in Parallels. I had to do 2 things:
-Upgrade to the latest Parallels version (Build 5582)
-Under Edit-> Virtual Machine... choose Video then check off, "Enable DirectX Shaders (experimental)"
This gets the program to run very well without rebooting out of the Mac OS.
I'm doing this on a MacBook 2.16 gHz with 1 GB of memory.