Once you are very familiar with any CAD system, its hard to break away. AutoCAD is not a bad platform I reckon, its just gotten too many ways of achieving the same goal, and too many (albiet often needed)options which baffle many, yet comfort the experienced users.
I dont think its different if you were moving from any CAD package to another one.
From what Ive played with so far using Inventor, its very clean and easy to manouvre around the menu's....I think theyve got a smashing layout there on the whole, and beats a lot of other software for intuitivity. Theres even design doctor and flag up references on unfrequent or new commands.
I reckon it would be very easy to learn, however, as with any MCAD package, the mindset of sketch>constrain>model>assemble>3d constrain>documentation from just 'drawing it' is the real transition.
See ya
Sirius2.