As for answering the actual question, everything is done on my mobile phone, business cards and facebook. Everyone I know well (close friends, housemates etc) are on my mobile. All my aquaintances from university I keep touch with on facebook. Facebook reminds me of birthdays and tells me what their up to in my news feed. Finally I keep all my business contacts in piles of business cards on my desk. One pile for archive, one for people I need to contact soon and one for people I'm awaiting response from. I can even easily tag people by writing metadata on the back of the card.
http://www.37signals.com/svn/posts/265-preview-1-an-introduction-to-highrise-the-product-previously-known-as-sunrise
But I'm *awful* at maintaining friendships, networks, and things for that nature. So I'm not a good person to take advice from on this.