There are a number of services online that make an "e-penis" list of the things I've listened to, read, played, or watched. I religiously update both my Shelfari and MyAnimeList accounts, and Last.fm takes care of itself as does Steam. I'm trying to find a comparable site to keep my movie reviews and ratings, and I was using Flixster on Facebook until I logged into the application with my actual Flixster account and it deleted the year and a half of ratings and reviews I had made while not technically "logged in." Great feature. IMDb is likely the place to go, and Mashable put out a list of 10 top social networking sites for movie lovers.
I'm both curious and squeamish about exploring what makes these kinds of sites so addictive. Squeamish because I'm afraid all I can point to is they help me feel like I've done something "productive" with activities that might not otherwise be considered "productive". Sure, I just logged two hours in Team Fortress 2 and grabbed a handful of achievements, or I finished three more episodes of Nodame Cantabile, but I could have been spending that time studying Japanese. I can't help but come to this conclusion because I also tend not to be very social on these sites. Sure I've got real life friends on Shelfari and Steam, and I keep an eye on their updates, but I'm mostly content to see myself chip away at the massive list of films I haven't seen or books I haven't read.
Is there inherent value in having these lists? Beyond justifying how I spend my time and sometimes not being able to remember all the media I've consumed.