The first rule of being a passive hacker is... ;) That being said, they are all over. I find too many and I can't act upon them all. I've always had an interest in business models and successful companies/people in "non-sexy" (to most of the HN crowd) areas.
Sometimes it seems that everyone is all wrapped up in solving first-world 20-to-30 age bracket problems (social, picture filtering, SaaS for other 20 to 30 year olds, etc). Nothing wrong with that, but there is so much more out there. IMO, it is way more interesting and has much more impact on peoples lives.