Just make sure if you have shared folders that they are password protected. You can read the discussion on
war walking for a fairly intense discussion about people that might be trying to get onto your system but my feeling is, even if someone comes across your network, the most likely thing they will do is use your internet connection.
On the third page of the above thread you'll see a fairly extensive post that I made. At the bottom of it, you'll why I use the security features.
In the meanwhile, enjoy your WiFi (at least until someone comes up with some doomsday scenario that will cause you to shut it down).