One thing that I'd like to quote from the original article is the paragraph on Enterprise Software:
Enterprise software companies sell bad software for huge amounts of money. They get away with it for a variety of reasons that link together to form a sort of protective wall. But the software world is changing. I suspect that if you study different parts of the enterprise software business (not just what the software does, but more importantly, how it's sold) you'll find parts that could be picked off by startups.
One way to start is to make things for smaller companies, because they can't afford the overpriced stuff made for big ones. They're also easier to sell to.