I was just intoduced to Inventor 10 in October last year and I have never used AutoCAD or any other CAD software.
I imagine that Inventor is the most "user-friendly" as was stated above, most of what I know I had to teach myself. Being a teenager I did not refer to any of those lame tutorials
It went pretty well and I know enough to cheat the program into doing what I want it to most of the time.
However, I have noticed that Inventor doesn't like it when you organize your work into sub-folders. I like to keep my computers organized but inventor has trouble finding the path names when i put parts in subfolders. This leads to many whiny pop-ups demanding pathnames whenever I try to open my project and seems like an oversight on the designer's part : /
Another problem I noticed was the frequent errors and long pauses as the program does god knows what after I tell it to perform simple funtions like contraining two objects.
Overall I think i would be much happier using a pencil and a ruler than using this program and I probably wouldn't mind investing the time to learn a more "drawing oriented" program like AutoCADF or ProE which (I'm assuming) have more of a coordinate-plot / layering interface.
Basically, I can't imagine anything being "worse" than inventor. Alas, thats what they give us and I don't have a couple grand lying around to invest in a professional CAD program.