My network requires a security key, which luckily I printed the paper years ago when I set up the router so I'd have a hard copy of the settings for future reference.
Which meant every flipping time I'd have to reset my brother's ancient computer (the one he had before his current one) I'd have to dig out the sheet.
And I don't think there's room for anyone else to try to squeeze in either. We've got a desktop PC, 2 laptops, a wireless printer, PS3 and iPhone that all run off the same router. We don't share.
I do this for the house's wireless network. I keep a sheet of paper with the WEP key for our network stashed in the desk. Any time we have to add a new device into the system (laptop, gaming console, etc.), or re-add it to the system after some glitch or other, I grab the sheet and enter the code-- or give it to the family so they can enter the info.