Opensource.com has an interview with developer, writer, and entrepreneur Andy Hunt. Andy has been in the business for a long time, and has seen the evolution of software through the years. According to him, proprietary software in the datacenter and enterprise desktops has had its day, and is on its way out.
My experience suggests that Andy is right, although it is important to recognize that not everyone agrees. I have spoken with many sysadmins who still swear by Windows servers, and many more who swear by one proprietary Unix system or another. However, it is also worth taking those opinions with a grain of salt, it is almost impossible to convince a person of something when their job depends on them not understanding it.