I built the initial foundation for my Ruby/Rails consulting career on the back of my eBook. That opened up the opportunity to work some awesome people (directly, as in "I read your book, work with us") and to write a book for a "real" publisher. Of course these opportunities opened up more work and conference speaking opportunities.

And again this past year with the Rails 3 Upgrade Handbook. I was invited to speak at like 5 conferences based off my work on that along with some other opportunities.

So yes, getting information out there in a cohesive way that people are interested in is a great way to open up opportunities for yourself, whether it's a blog, book, documentation project, etc.

Ditto here, particularly with regards to blogging. Community participation also has helped me, although it was one of those "overnight success in five years" stories.

My iPhone user interface tutorial site that I launched a few weeks ago has already spawned 3 book offers: 2 from O'Reilly, 1 from another publisher. I politely turned them down: I'm fortunate to have a fairly sizable audience, so traditional publishers can't offer me much. I'm not going to lie, telling editors at large publishing houses that I'm more interested in self-publishing was more than a little satisfying.

I was offered a gig being the co-writer of a book on Python by Manning. I turned it down ultimately for a variety of reasons, but in part because I thought it would be a lot of work for the likely pay, and partly because there were (what I considered to be anyway) several good and free alternatives already. Looking back, I might have accepted and done it, because I have heard it leads to more publicity and helps you get more paying work, which indirectly compensates for it. You asked about whether blogging might have created opportunities. In my case, I think it has, I know I've had folks look both at my writing and the rest of my online presence and that was a big factor in getting new paying work and opportunities. Everything helps. Just giving tangible evidence that you Have Skills and can Get Things Done, in whatever field, is huge.

While not specifically about eBooks, the 'Conclusions' section of this post http://beginningruby.org/what-ive-earned-and-learned/ by Peter Cooper does a good job detailing why one might - and might not - want to write a book.