I've had experience successfully selling my own books, and in marketing some self-published books by others. A big rule you need to apply here is essentially appropriateness to the market...and the means of marketing.
You don't self-publish a best-selling novel. On the other hand there are lots of types of books that can be niche-marketed. I knew a guy who wrote a guide to Spanish for restaurant workers. (Clever book, and it had two front covers...one half span to eng, the other half eng to span) He marketed it through the restaurant supply network and sold a LOT.
Another guy I knew before he suspiciously disappeared off the planet wrote a guy to prostitution in the Dominican Republic. Sold or $25 on the internet...he was making $600 a month. This is an obvious choice for narrow niche internet marketing.
I helped a friend start up a book on how to do firedancing.
One of my books, Mexican Slang 101 was created to be sold by little boys on the beach, but ended up getting wholesaled, then sold from an internet site, using ebay as the business end.
That is a great way to do it, by the way. If you know how to put up a website and promote it, then use ebay as your "store" and Paypal as your cash register, you can double your profit off the book. Modern technology makes printing cheap...a little knowledge of how that works can cut your costs a great deal. (Two of the books above are produced on Xerox, then bound, by the way...an acceptable quality level in some niche markets and requiring no big investments in printing up front.)
So i you are doing the right kind of book, there are possibilities. And it doesn't have to be a how-to or smut or clandestine stuff, either. I could see this working for a book on the Tibetan-American experience, short fiction about Lesbian love, a novel in the tradition of Quintin Tarrantino's films...anything where there is a community that can be dialed into fairly surgically on the internet. Screenwriting would be a good bet: a sexy, outrageous roman a clef about a screenwriter faking identity on the internet....
The same would hold for podcasts, though I am not experienced in that. Off the top of my head: how about downloadable files that lead cruise ship passengers on destination tours--explaining the main sites, a drop of the language perhaps. A talking guidebook they could tuck into their iPod for their trips ashore in Mazatlan or Freeport or Venice or wherever. And since there are a couple of websites that very tightly target cruise passengers...it would be worth a shot.
How about a podcast of your home city, made available at hotel newstands and concierges?
So don't fly into rapture at mention of the Brave New Pardigm, but don't let naysayers turn you off if you have something that can fit into the "receptor site" of the world market. If what you're doing fits...or if you can scheme up a way to make it fit, it's worth a shot. Most of this is about time and good thinking and doesn't require heavy financial investment up front like printing 5000 books then trying to flog them.
By the way...all of the books I mentioned are the type where fancy looks mean nothing, but low cost is extremely helpful. I actually used repeated Xeroxing to degrade the type face of Mexican Slang's first editions, so that it would look more like scruffy underground info.
Another tidbit...the Dominican Republic ho-hoppers book cost about the same as mine to produce, but sold or 5 times as much. The more pressing the need you fill, the better the rake-in.