Although this admittedly isn't my specialty, I would imagine that they only generate worthwhile income if they have a fairly significant amount of traffic. Ergo

Although this admittedly isn't my specialty, I would imagine that they only generate worthwhile income if they have a fairly significant amount of traffic. Ergo, it's not as simple as "put ads on this domain name and wait for profit," but instead would require getting traffic to your site (which most people in that industry tend to do by spamming). It's definitely possible to turn a profit, but it's not as simple or clean-cut as you might believe. That said, sex.com just sold for $13 million, so if you happen to land on something good, you're probably in the money!