I actually think it's fine to spend time on HN, you just can't also spend tons of time on tons of other sites as well.
Based on anecdotal evidence only, it seems the rate at which articles move up and down the HN frontpage pretty much ensures you'll see everything that hits the front page per day if you check HN twice - once in the morning and once in the late afternoon or evening.
I don't think that's too much HN browsing to prevent you from being uber productive, as long as you're not also browsing tons of other sites on the net too.
