Also, RMS always (at least in the book) categorized himself as a hacker, but writing an OO layer over and RDBMS doesn't seem to be quite as complex as rolling your own C compiler suite (or say, writing your own language interpreter for a your new language based on C, sed, awk...you can see where I'm going)

Point taken with respect to project complexity, but I guess I just wouldn't call those types of projects 'hacking' ; )

...so complexity, scale and planning really wouldn't seem to be an issue either

Scale and complexity, no; planning, yes. To my mind, the critical difference between hacking and programming is the amount of structure and forethought that have gone into the undertaking. Now, RMS may want to call himself a hacker, and claim that all his software projects therefore are acts of hacking, but IMO this definition is too broad. That's why in my formulation I stress that hacking involves a deviation from author intent or preexisting structure of the codebase, or is just plain old screwing around.