Well, I surely don't know all of the subtleties involved. In fact, I'm quite sure nobody does. Again, I'm being US centric here, but our tax code is pretty absurd.

You can download a copy here: http://www.gpo.gov/fdsys/pkg/USCODE-2011-title26/pdf/USCODE-.... I've read in many places that the US taxcode is > 70,000 pages. Maybe that includes state taxes. This pdf is a little over 3000 pages.

Still pretty complicated, and makes plenty of room for maneuvering in tax avoidance efforts.