So long as you've got some sort of wireless encryption going on, it helps quite a bit. For the paranoid people, WEP is rather weak. AES/TKIP encryption with a "keyword" (it's used to generate the encryption key) that isn't a dictionary word (mine is a scramble of Erika's, mom's, and my passwords all rattled around) is one of those military-strength things that will keep people from getting into your network from across the street.