Having worked in AutoCAD before Inventor, I got in the habit of leaving off the inch mark (") on my dimensions when typing them in. Inventor can't seem to comprehend that.
For example, I should be able to type in 12'3 and Inventor should know that I mean 12 ft, 3 inches, without having to type that final quote mark.
AutoCAD can do it, and it's so frustrating to keep getting an error message for invalid dimension for something so simple that the program ought to be able to do. Less keystrokes = better.