I can spend hours on Reddit while I only seem to spend a few minutes on HN. On Reddit I go from /r/programming to /r/diy to /r/art, besides just looking at the first page. On Hacker News I only look at the first page. Once I've gone through it, I'm off to Reddit. The first page doesn't seem like it changes that often, so I only check it once a day or so.

That said, the discussions on HN are usually about technical topics from technical people. It's far more intellectual than Reddit where a lot of the comments are puns, jokes, and other off-topic nonsense.