My issue lies with the content weight on hacker news - a lot of posts require 3 mins+ to read and grok, potentially explore related concepts/sites, and maybe even try out a product. I'd say about 50% of the posts on HN interest me enough to warrant this kind of attention. Then of course you have to read the comments ;) This can eat away a serious amount of time!

It also doesn't help that this time can be labelled as "productive" in my mind (as opposed to Facebook etc), when in reality there are more productive things to be doing in these moments.