I spent a few hours during the course of a week last year and got 1000 in reputation. Most of the points I got were from quickly writing answers to boring questions before someone else could get around to writing an equally good one. I did get some points from going above and beyond, or from answering questions that hadn't been answered for a long time because they were from a niche I was familiar with. I suspect that most of the people with a lot of points are treating it like a game, though.