Selling domain names has always been around of course, just at varying degrees of price. After the dot com bust domains were generally accepted to be worthless, today not so much.
For the last few years domainers didn't pursue domain sales because PPC revenue was quite robust. In the last year as PPC and traffic stalled against a backdrop of changing ad platforms, smart pricing and discard rates; a funny thing happened... people started selling names.. and for a lot of money. Then Fabulous came along with their DDN laying the track for a sales network which will change things for years to come.
I see us gradually returning to the beginning when domainers made a significant tranche of their revenue selling their names.. doing that in tandem with PPC and traffic arbitrage until the next generation of higher revenue domain name related paid-search sorts itself out.
The industry rule of thumb with large domain name portfolios composed of generic long-tail keyword style names and search terms is: you can make one dollar in domain sales for every dollar you make in paid-search. I have seen this characteristic across several large portfolios. It's one of the reasons I'm so bullish on Marchex's break-up value. If you're not selling domain names that represents an untapped revenue stream. The problem of course is that you can't replace the good stuff quickly enough and you risk selling the odd name too cheap.
I think developments in the sales industry will help sort these problems out. If I look ahead 5 years I see a mix where half a large domain portfolio is held for a name-sales marketplace focused on the trading of names, the other half is structured like Netshops or a lead gen network, utilizing organic name type-in traffic to high quality domains, coupled with Geosign style arbitrage to bring extra traffic to those netshops style sites which teams of people work on building out. Something like that anyway.. Perhaps there is another leg where semantic technology helps to enrich these sites with dynamic content which is friendly to the search-engines or with wikipedia style pages which serve to create user generated content.
Bottom line, there are so many ways to peel this banana.. but the heart of what's inside is very tasty and good for you :) .. The more we come out with new ideas about the future, the more those ideas rhyme with the past.