Yes, I keep a database on people. ;) I use an Emacs module aptly
called the Big Brother Database (BBDB), which is just a keystroke away
from my mail (Gnus) and my blog (Planner). I keep all sorts of notes
in it, like when I met someone or what their food preferences are.

The following bit of Emacs Lisp code extracts all the names and e-mail
addresses from my BBDB. I have 1852 distinct e-mail addresses,
although a number of them are not for people.

(mapc
 (lambda (rec)
   (if (bbdb-record-net rec)
       (let ((name (bbdb-record-name rec)))
         (mapc
          (lambda (addr)
            (insert name "\t" addr "\n"))
          (bbdb-record-net rec)))))
 (bbdb-records))

I uploaded the list to LinkedIn and
OpenBC, my two favorite business networking
sites. I found that a lot of my contacts had joined the services since
I last checked. It was great being able to refer to my notes and make
those connections. For example, one record said that I'd met someone
in 2004 at a Tokyo Linux Users Group meeting – something I'd probably
not have remembered on my own…

Some of the records didn't have much annotation aside from the note
“personal mail”, which means I probably should set up mail indexing
and search again. Hmm.

It's nice to have these notes at my fingertips.