Brian Laung Aoaeh, Aartner at KEC Ventures just posted a great deck on startup barriers to entry, or ‘economic moats’ as he characterises them. When you want to think about building a big company, some way of fending off the hordes from undermining your supernormal profits in the medium term is sine qua non.
In my opinion ‘network effects’ are the only true startup barrier to entry, at least in software. He deals with these in pretty good detail, before then digging into other areas such as patents and cost benefits. If you are a neophyte to this area, this really is a great primer, furthermore, more experienced hands will have a thing or two learn too.