My opinion's just the same as Naomi's: for niches of either subject or area (books about the local walks, for example, or breeding fancy budgies) where it's relatively straightforward to get the whole potential market to know about the book, it can work well, though you're still unlikely to make much money, and probably none if you cost your time spent producing and promoting it. For everything else, it's highly unlikely to work. And it also scuppers your chances of ever getting the book published commercially, since generally speaking they're only interested in brand new books. As Naomi suggests, IF you did manage to sell tens of thousands of copies off your own bat, it might be something to mention in trying to get your next book taken on by an agent or publisher, but otherwise I'm afraid that to the book trade it simply doesn't register. Worse, because they see so many appallingly written and produced books published by people who don't have the first idea of how to do it properly, perhaps unfairly, having self-published could even be a minus against your submission.
This is a good collection of blog posts by a former publisher's-editor turned writer:
http://howpublishingreallyworks.blogspot.com/search/label/self-publishing
Emma