I have a MySpace account purely because I have a few friends on there, and have had to use it to send the odd message once in a blue moon. I hate the way MySpace looks - it's cluttered, slow, gaudy, clunky, and I just don't like it.
When Facebook came around, naturally, I signed up. I was pleasantly surprised. It had a clean design, fast, plenty of AJAX used in the interface meaning fewer page refreshes. I could quickly and easily find out what my friends were up to.
And then Facebook allowed applications to be developed for the platform. Now everyone throws sheep at each other, I'm constantly plagued by vampire invites, being bitten by werewolves, being compared with others, having films and books recommended to me, having things posted to my FunWall (which I don't even have) and thus the torrent continues.
If I actually want to become a werewolf, or see what's been posted to "my" FunWall, I have to install an application on my account. I have to let it see certain information about me. It will clutter my profile.
If I allowed every invite to install the required app, my profile would be worse than MySpace.
This post over at Mashable sums things up rather well. I too am suffering from 'Facebook fatigue', and the urge to log in is dissipating rather rapidly...