Jason Fried and the team at 37Signals put together a free eBook on building a business based on a web application. I thought it was pretty neat considering they have experience in the business and few entrepreneurs seem to spend the time to really document the process and the pitfalls. I have not read the book but the table of contents suggests that it is full of practical advice, and Fried has a good reputation in the web application business.
Of course this is released the same time as Paul Graham writing an essay noting that observes startups are moving towards hardware products. I am more of a software guy than a hardware guy myself, but I enjoy gadgets. I am fascinated by 3-D printing and some of the other technologies coming out of the maker movement, but the downside of hardware is that it usually requires more investment than software. Therefore it becomes a more expensive hobby than programming and also there is greater risk if you try to scale hardware into a business. For that reason I have a lot of respect for the hardware guys.