darn fork lock. After returning from Central America last month, The first thing I noticed was the cover on my bike ripped to shreds. A note from my neighbor stated that "hurricane force winds blew my bike over 4 or 5 times, and the guy down the street picked it up."
Shortly after discussing the event, my neighbors said that they would've moved the bike in their yard, but were unable to because the fork was locked. OK, so that was an extraordinary situation, and perhaps an extreme example.
Really though, if you don't want to shell out the $$$ for a locksmith, the alternatives mentioned previously in this thread will work just fine. Well, it also depends on your neighborhood. If my bike was parked on the street in some neighborhoods I could think of in Manhattan, It would be covered with armor and welded to a light pole. Some thieves have a tendency to remove parts also, not just the bike