Here's a nice article about author Scott Kelby in USAToday. It refers to the "$20 million empire" he has built around books, magazines, conferences, etc. The article opens with a note about something I've said countless times to new authors: "You can't get rich writing computer books." Actually, a small number of authors have, but they represent a tiny percentage of the total author population.
One of the lessons learned here is the importance of diversifying your efforts. Books are a key ingredient, but Kelby has done a fantastic job getting into other areas of the industry. It certainly doesn't hurt that he's now extremely well-connected within Adobe, of course!