Paul Carr’s current “NSFW” column (which is entirely safe for work; NSFW is just the column name) focuses on the recent announcements by authors such as Seth Godin that they are leaving traditional publishing to go it alone. Carr, who is very happy with his publishers (though it’s possible one of his publishers might not be happy with him), devotes a quite lengthy article to rebutting point by point the arguments in favor of ditching publishers.
The article is quite long even to summarize, but a few of the points Carr covers include the issues of quality and editing, the added credibility that comes with having had books issued by professional publishers, support for things like marketing and copyright enforcement, and the differences in relative market size.
Carr suggests that leaving publishers in favor of self-publishing makes sense for only two sorts of people: those who are already skilled marketers, like Godin, and those who fear they’re about to be dumped by their publishers anyway and want to save face by claiming to be “innovating”.
I suspect that, as with most things, the truth lies somewhere in the middle. In any event, the next few years should reveal just how much sense self-publishing makes for most people.