Facebook Friends

What is your approach to adding friends on facebook?

Do you have a 'rule'? As in, I won't add anyone who I haven't spoken to in x years? Or, I won't add anyone who I have never met face to face?
I have seen a couple of familiar names/faces from the blogosphere who I haven't added for that very reason.

Scrolling through some friends-of-friends-of-friends recently, I came across someone I knew from a few years ago. It would be hard to 'define' our relationship - but it would be somewhere between 'colleague' and 'passing acquaintance'. Anyway, I wasn't sure whether to add them, so I didn't.
A few days later, I saw this same person walking through town at lunchtime. I walked straight past them and made a half-hearted attempt at eye contact, but apart from that , there was no interaction.

Is that a sign that I made the right decision in not adding them? Or do you think, maybe if I had, we could have had a long and meaningful catch-up conversation?