Final Fantasy XI had the Vana'diel Adventurer Recruitment Program that gave out goodies the longer you and your friend played.

I think Final Fantasy XIV needs a similar recruitment system in the near future. The rewards were kinda cool, you could receive the costume belts, and HNM statues.

If you have no idea what I'm talking about: http://www.playonline.com/ff11us/guide/recruitment01.html