Had it not ended up so long, the following was meant to be left as a comment on Don Park's Improving Open Source UI post, which is a response to Eric Raymond's rant on the problems of open source UI, The Luxury of Ignorance: An Open-Source Horror Story. (Also related and of interest, Raymond's Part Deux follow-up post and Jon Udell's response Aunt Tillie's OS X adventure.)

I don't think the ethic of the software development process (even especially in the loose group nature of the open source process) very much resembles the ethic of the aesthetic design process.

As part of the significant cultural differences between software developers and (aesthetic) designers, each culture has very different concepts of things like how groups of people work together, how their work gets specified and reviewed, how decisions are made, and how revisions occur.

In other words, I don't think the software development process itself tends to produce good UI design. Rather, software with good UI design comes out of a kind-of authoritative strategy to produce that through (relatively strictly) managing a larger process of coordination between developers and designers (and others).

Commercial software maybe has better UIs because, within its "cathedral" process, it is probably more often possible for someone in charge to coordinate the positioning of IA / HCI / UE / UI designers as senior to software developers when it comes to making decisions about certain types of design issues. (Obviously, much commerical software also fails to realize good UI design.)

I also wonder what Raymond supposes about the "UI" of real world bazaars. In my own experience, I would say that navigating and getting desired results out of bazaars requires initiation in the "code" of the bazaar. Cathedrals seem to be all about guiding the "user" to specific results.

I don't mean that people need to know how to write code to use open source software, but I think most software expects people to understand a lot of technicalities and protocols. Good UI helps people learn those quickly whenever that is required—especially by teaching people a small set of basic principles that are applicable in many interactions. (In this sense, many Unix commands are designed to be good UI for command line users.)

Note: for those that might not know, Eric Raymond wrote the excellent essay and book-to-be, The Cathedral and the Bazaar, about how and why open source development is different and great.