I use the dinky little Dakine locks that fit in your pocket that have the 3-digit combination lock. Honestly, if someone truly wanted to, they could cut through them with a large pair of pliers, but I doubt few would go to such lengths to do so when there are so many unlocked boards around. I always keep that lock, and I have my wife take one as well.
In short, $10 insurance for sometimes up to $700 (MSRP) of gear? Cool by me.