It depends on how noise the wireless network is but with on AP and one client node, WEP can be popped in less than five minutes. If the network is nice and active, you may not need the active step of forcing the under five minute method; sit passively and quietly waiting an hour and your in.
It is persistence and patients that inevitably opens networks or keeps levels of security high.
WPA can also be popped but it is still multiples harder than WEP. Given the amount of effort it can take, WPA2 is generally considered the minimum safe standard. Use of random keys rather than passphrase (WPA-PSK) is even better.
I think it's about time I threw the spare router into a wall socket with SSID = "hackthissucker" (well, something similar to that but more obvious of course

) just to see who in my area wants to play. If I fully trusted virtual LAN separations, I?d even attach the secondary router to an outside connection and see what people are foolish enough to move over an unknown network. My primary router may start getting random 8 char SSID (mostly for fun) and the maxed out random passkey is going to take longer than my change interval to pop.