I learnt all the basics on MS flight sim, but soon found navigation (visually) quite impossible as everything looked the same so once i got into the real thing i gave up on simming.
but before starting on the IMC course i tried some IMC stuff in flight sim and infact continued doing so during the course, i found it very useful for all the proceedural stuff, like holds and approaches, as well as little things like remembering morse code and remembering to start the stopwatch.
more recently i've been attempting aerobatics on flight sim (as i dont have the money to do much for real) but since its almost impossible to spin any of microsofts aircraft i've had to download a few, my favorite being the super decathalon which i would love to fly in reality now, if only i had money.
Owen