VoodooPad source license?
His response is very encouraging! I hope other developers feel the same.
This morning I noticed that the four applications I want the source to are all writing apps, or closely related to writing. OmniOutliner and VoodooPad are purely writing applications. Sid is a writing application for Conversant weblogs. NetNewsWire isn't purely a writing application, but it has two writing components, the weblog editor and the notepad. I'm not sure I'd want NNW's source to change/improve the writing components specifically, but I have a lot of other ideas for NNW.
As I was writing this, I was thinking of what other benefits developers could get out of having a source licensing program. Having a private developer community sprang to mind. People who bought a source license would be allowed to subscribe to a private mailing list that only other source licensees were on. Licensees could share ideas with each other, help each other add the features they're trying to implement, etc.
(Rambling now...) I can see this being a bit of a support headache for the developer, if the licensees asked too many questions or requested too much free support. I think the developer could help themselves by setting clear expectations of how much time he/she was willing to spend on the list answering questions or participating, or by also setting up a paid support program in addition to the source license program. (end of rambling)
So what would a developer get out of this? Well, imagine if you had one or more of the following developers purchase a source license and be an active participant on the list: bbum, sabi, Mike Ferris. I think a developer could learn a lot simply by following a discussion where these people were discussing different aspects of your codebase. And I think the other licencees could get just as much out of it. And if you ever needed to hire another developer, either full time, part time or for a short period, you'd have a good stable to pick from.