Interesting; I've encountered "yak shaving" as meaning something slightly different: it's when your main task depends on a subordinate task which is long, difficult, and stupid--e.g., in programming, it's something which the tools should be doing for you. (Bonus points if you know that, on a different OS, or in a different language, the tools would be doing it for you.)

The original MIT meaning is closer to what I recently heard described as meta-yak-shaving, which is when, before you can start shaving the yak, you discover that each hair of the yak contains a subyak, and each subyak has to be shaved individually.