Publishing technology books, especially related to any online tools or programming languages is a very fast paced, and dangerous, situation. Books take years to produce, write, publish, and distribute. More than likely, if you started writing a book on the newest technology now, it wouldn't be out until mid-late 2007. During this time, the tool or language you are writing about will be in a new version, used in new ways, and be sitting next to 5.4 x 10^6 books on the same subject on the bookstore/library shelf.
Magazines deal with this problem by publishing on a month-to-month basis. But an article can still take several months to publish and is limited to several pages, at most, in length. Not enough to cover an entire language/tool.
The answer, currently, is to publish online, early-editions of your books. Push them to excited "beta" (so Web2.0) customers who are willing to pay for up-front copies, and give feedback to the publisher. This is similar to a beta program for the commercial Operating Systems. Developers want information now.
Pragmatic Programmers Beta Books was the first of this genre that I am personally aware of. You can purchase the PDF version of the book now, and get updates for the lifetime of the book. They are currently offering Rails Recipes and Pragmatic Ajax: a Web2.0 primer ($20.00 pdf/$37.45 both)
Manning Early Access Program (MEAP) (did I just hear Beaker?) is offering Ruby for Rails: Ruby techniques for Rails developers ($22.50 pdf/$44.95 both), which looks like quite the tome, at 600 pages. This seems like an extra reason to get a veritably 0g digital copy.
O'Reilly Rough Cuts, is a bandwagon jumper. They already offer all of their books in online format via their 'Safari' service, but charge extra now for their version of the beta books. In addition, it appears that when you pay for the beta book, you only get access to it until it is published. You then have to buy the full copy when it is released. They are offering a Ruby, Ruby on Rails, Ajax, and Flickr books.
I like the idea of getting access to books now, rather than waiting for eventual, and typically belated, publication. By using a digital, 'published' book, I can use a more trusted resource than your various flavors of search engine (and often tainted responses - which tend to propagate bad coding practices). I don't have to keep an aging, dead-tree copy of a v1.0 (or 2.0) book on my shelf and look at it years later and laugh at how out-of-date that language/tool is now (you go with your BASIC and setting up the TRS-80 books).