Google "Ask a motorcycle thief", it was the best 2 hour read I've had on the subject.
A couple of points:
- A disk lock on the rear is much more effective than on the front, harder for a good thief to swap wheels. More awkward to work on.
- Bring a stubby screwdriver or appropriate hex, remove your clutch lever. The likelihood of a thief carrying spary clutch levers / perches would be fairly minimal.
- Outside of an apartment building seems like the single worst place to leave a bike.
- Don't leave spare key or ownership in trunk.
- Always lock steering.
http://rideapart.com/2012/05/ask-a-motorcycle-thief/