Marrying your best friend seems to be the way to go...
I have to agree with you OBG. Knowing my wife as my best friend for around 14 years (she knows the exact length - I think i'm close with the 14 year mark), then 2-3 years together/married.
Having your best friend as your spouse can't be beat. Been through a tonne of crap with each other as friends and she still wanted to be friends afterwards. Says something about someone.