I have published four books with O'Reilly, and I have had brief encounters with other publishers. As a book consumer interested in cloud computing, Java, scripting languages, I look to Manning, Prag, and O'Reilly most of the time, and I'm also impressed with books from AW. Here are my experiences, maybe they might help:
When I wrote Jakarta Commons Cookbook, I had no agent, I worked directly with a great editor, Brett McLaughlin. Brett has since moved on from animal books and is now focused on books in the Heads First series. I would have never finished my book was it not for Brett's attention and guidance. If you are new to the book writing process, you will want to find an editor who knows your technology and who believes in the idea behind your book. I had maybe 5 reviewers, the book sold something in the range of 6-7k. While the publisher didn't view this as a success, I was satisfied with the sales and exposure, and I enjoyed the writing process. This book was written in Word, to properly insert XREF (cross references between sections and chapters) I had to load the entire book into Word and then run some hefty macros. I was constantly freezing the machine and Word was much more a nuisance that a helpful tool.
The second book I wrote as "Maven: A Developer's Notebook". To say it didn't go so well would be a dramatic understatement. I was less that satisfied with the book writing process, there were too many reviewers. Part of the problem with this book was that the book covered Maven 1 which was already on its way out. Maven 2 was released the same week that this book on Maven 1 was released. Sales were not very good; in fact, less than six months after printing, a number of people (myself included) were recommending that people avoid purchasing this book. I didn't actively seek out this second book, that should have been the first warning sign, I was recruited by my editor to help smooth out the writing. This book was written in Word using the O'Reilly macros, we had endless problems with Word. I had an agent for this book from Studio B, and the only time I spoke with my agent was during the contract negotiations. Studio B is "ok", but I don't think you need an agent to write a book, maybe someone can convince me otherwise?
The third book I helped to write was also something that my editor suggested. Jim Elliott was updating Harnessing Hibernate, and they wanted someone to write some chapters on Spring integration. This was my first exposure to using XMLMind and editing DocBook directly. Jim is one of the brightest authors I have ever worked with, and his colleague Ryan Fowler and I quickly started to use the DocBook XML from the first edition to update the book for a Second Edition printing. The writing process was a bit prolonged because two of us had some big distracting "life events" during the writing process. I'm proud of the end-product, and writing the book in DocBook was an eye opening experience. I would suggest that you get into the "craft" of book writing, code the book in DocBook using something like XMLMind, learn how to create and index, learn what it takes to create a book with all of the necessary markup. Writing a book is an entirely different beast from throwing some words into a Word Processor, and there's something to be said for understanding the entire process from start to finish.
The fourth book is an almost entirely different beast. Because of my experience with Jakarta Commons Cookbook and Maven: A Developer's Notebook I didn't want to be involved with a book that wasn't open source from the very beginning. The fourth book I'm involved with is Maven: The Definitive Guide, it is a comprehensive reference for Maven. This book is available for free from http://books.sonatype.com/ and you can also purchase a printed copy from O'Reilly. The book is an open source project on GitHub, the book is covered under a creative commons license, and we've attracted a global team of people who are translating the book. There are still some conflicts between the idea of giving away a book for free online and selling a printed version, and I think there is still work to be done at speeding up the pre-production process. The biggest difference between the fourth book and the first three is that it is an open source book which has a life beyond print, it is much more satisfying to be involved in a book that can be constantly updated and which can attract a community.
Disclaimer: I'm partial to O'Reilly books, I grew up reading my father's programming books and I'm also an infrequent contributor to the website.
"The more that came out, this was before he'd even given up the passwords and so forth, the stories I was reading and the information I was able to glean from, the court records, etc., was sending up red flags all over the place. They were claiming the now famous 1100 modems that they initially said Terry Childs may have planted around this city and a whole host of other things that just didn't jive."
Venezia writes in "Could the Childs case put all network admins in danger?":
...if Childs is convicted on the modem charges, then just about every network administrator in the world could be charged with the same "crime." You might as well start arresting carpenters for carrying hammers and saws because they could be used as weapons.
Porsche: there simply is no substitute. -- Risky Business