We're currently doing this for EtherPad. We added a "pricing" tab to our homepage, but we don't have any prices yet, just a sign up form. So far (2 weeks in), about 100 companies have signed up to hear more about our for-sale version.
Because I plan to use it with my customers I knew I wanted to pay for a supported SaaS/hosted version. I have been surprised that we have been unable to have any meaningful discussion about it. I know that one interested user doesn't constitute a market, but I was dismayed with the lack of meaningful engagement beyond we will notify you when it's ready.
I think the part that's was left out of the Venture Hacks article was when someone tells you they want to buy it, have a conversation with them to understand how they plan to use it and how they value it (what are the alternatives that they are comparing it against).