There's a lot of talk at the moment that Amazon is forcing self-publishers to use its own publishing centers in order to stay listed with the powerhouse Internet sales site. For example, this blog post Has Amazon Gone Mad by Rick Jelliffe rather aptly describes the situation. The Writer's Weekly first broke the story here, but it's now been taken up by major media such as the Wall Street Journal. Blogger M. David Peterson points out that there are alternatives - simply print enough copies ahead of time and ship them to the Amazon printing centers.
This certainly isn't the death knell of publishing. But it is a telling sign. When I first started writing books, an author could reasonably expect to sell the first printing of their book, probably about 5000 books. This was usually enough sales to cover the advance that the publisher paid them and maybe a bit extra to cover a celebratory round of beers with his/her buddies. If the book was good and the the stars were in proper alignment, the author would be lucky to get addition printings of their book out the door and actually make a little money on the project. Nowadays, it seems like the first printing of a new title is only around 3000 and fewer books seem to be ascending to the level of "strong seller".
Of course, there is always a place for titles like Word 2007 for Dummies. Those sort of everygreen titles will always sell. But it appears that the more niche your content is, the worse it will do as a book. The obvious reason for this is the Internet. Why would someone spend $40 for a book on SQL Server query tuning (as an example, I'm not knocking any specific book), when you could simply subscribe to the RSS feeds at sites like SQLblog, SQLMag, or SQL-Server-Performance and get nearly as much content? For that matter, the power of a good Google search (and not Windows Live Search, imo) enables you to pull valuable content from all three of these sites in short order. Not only is your search more taylored to your specific needs, it's also more likely to be up-to-date with the latest versions, service packs, and nuances.
Authors like me are also concerned because the immediate alternative that comes to mind is writing and publishing an e-book. However, e-books seem to hold even less promise no than in years past. At least when you buy a book, you have a physical object that you own. You can take it on a plane and read it during that "turn off all electronic devices" stage of the flight. You can take it to the bathroom. You can share it with your team mates at work (hopefully, not right after taking it to the bathroom). E-books, though, have all the limitations of a book with none of the advantages of the internet.
I believe that as the hard-print media (book publishers, magazine publishers, newsletters, journals, and newspapers) continue to see shrinking audiences, the key to survival is tapping in to blogging and expert opinion. For example, the New York Times is doing extremely well with their Freakonomics blog, based upon the eponymous book (and a personal favorite of mine).