I probably don't spend much time on facebook, but I habitually load the front page pretty much any time I have an extra minute and can't immediately think of anything else to do. I think the lure is that it updates every couples minutes or so with something new, whether it's something directed at you, someone posting a link, or just someone talking about how their dog's cock turned purple and needs to go to the vet or whining about the snowmegeddon.
It's sort of like how back in the day you might habitually check all of the away messages on your AIM buddy list every couple minutes, even when you really didn't give a shit about what those people were doing. Facebook is the modern version of that thoughtless information accumulation. Twitter too.
