Books Before Bytes

I noticed the other day that O'Reilly has a new book format
for prerelease software that relies on planning for and making incremental
updates as the software is developed.  After
the software is released, the prerelease book and all of its updates are
cleaned up and turned back into a book with standard formatting.  It looks like a Silverlight 2 book is
being used as the test subject.

I think this approach is interesting as a response to how
quickly software is developed and then obsoleted these days.  Additionally, software is being developed
with increasing amounts of transparency. 
Customers get early builds and trickles of information long before the
official release date, and often while the software is still very
malleable.  By the time software is
stable enough to write a real book about it, you've already missed the best window
for publication for that release.