With the popularity of wireless technology increasing and the price decreasing we're bound to see a shift in the signal theft arena. Since information is being treated more and more like currency, the chance to steal information destined for a computer on a wireless network is going to be very tempting not only for hackers but for competitors as well. I do not believe that it will be a bigger problem in the future, just a slightly different one.
Encryption is bound to play a bigger part in wireless computing in the future.
Even though it may be possible to receive a signal not intended for you, it will be totally useless unless you have the encryption key or the technology to break the encryption code. There are already quite a few software companies selling encryption technology to make private communications a little more secure but even current encryption cannot offer total security. On a global level, governments are arguing about encryption. Some countries like China do not want their citizens to have access to powerful encryption. The U.S. allows for individuals to own and utilize strong encryption but not to export it.