Ever built such great rapport with a prospect or client that you actually became good friends?

I've become close acquaintances with a few prospects before, right there on the cusp of friendship but never really gotten close enough to a prospect or client that I would consider them a friend.

I've met up with them for non business related lunches and what not when they were in town or when I happened to be where they were but being totally honest there was always an ulterior motive there in maintaining a good relationship either for personal professional gain or just to keep the business relationship solid.

Curios if a business relationship with someone you've sold to evolved into what you might consider a decent friendship.