Well, tech books anyway. Charles Petzold has written an excellent post on the state (and the point) of being a technical book author in response to Jeff Atwood’s own post on how he found writing his first book now that it has found its way to the shops.
And Charles has it pretty much spot on vis a vis the experience and the rewards of producing a 700+ page book. And the comments to the post are pretty much in two camps : ‘I chose to write a blog’ and ‘why don’t you self-publish?’ Ironically, Charles is probably one of the few technical authors who could go the way of lulu.com or Amazon’s createspace.com because he is well known enough to have knowledge of his book spread by word of mouth. Others would include Don Box, Scott Guthrie (if he ever chose to write one), and Bill Joy. Perhaps Miguel d’Icaza. The self-publishing route is double-edged. If you do go that way, you get no advance up front but you do get a higher return per book (with some payment to the printer pay book depending on the company you've gone with). It’s also true that post-publication, a self-published book will require more support and PR effort from you to get people to buy it.
As someone who’s now 200 pages into his 13th book, writing it in the wee small hours with support from Red Bull, I’d add two more brief points to Charles’ words on writing. You Write Books Because That’s What You Like To Do. Writing a book makes you learn and relearn your subject. Which is also good.