It's certainly alarmingly addictive. Much more so than a newspaper. I've been wondering lately what to do about that. Any ideas? I considered shutting the site down for a couple hours a day. More people disliked that idea than liked it http://news.ycombinator.com/item?id=372593 but the vote was close enough that I might still try it.
I'm a strong advocate of hiding the karma counts entirely (for users, submissions, and comments). That greatly reduces the conditioning effect, not to mention karma-related drama and groupthink (as Surowiecki argues, crowd wisdom is best procured when evaluations are performed independently). Submissions and comments can still be ordered by net karma over time, as they are now.
Whatever you choose to do, I think there's a strong argument in favor of experimentalism. Especially since the site isn't a commercial undertaking and can deal with the occasional disruption.