I was in a pub in Manchester recently for my friend Chris's leaving do (he's got a job in Spain :p ). Somehow a brief discussion about Mac OS X got started (yes, OK I started it). Most people I've met who've used it seem to think it's great because:
1. The GUI is great.
2. It's really reliable.
This issue of reliability and security is a big one in the IT scene. Most users, especially those managing large corporate IT systems, would like an operating system to be virus and hacker proof. Being uncrashable would be a bonus as well.
Thinking about these issues reminded me of the Airbus A320. As you may know, it is too aerodynamically unstable to be flown directly by humans. The pilot operates the controls and a computer interprets these "suggestions" about how the plane should be flying. It does some very complicated maths and works out how to fly the plane safely. However, there are actually four computers doing this job simultaneously. Each one has a different hardware architechture made by a different manufacturer, with a different operating system from a different developer running each machine. The same goes for the flight control software. A failure in one machine should instantly trigger the switching of control to the next one.
This design was chosen to minimise the horrific chance that a computer crash would cause a....CRASH. It seems that many companies choose one OS for a particular application and put their trust in that. I know the company hosting my website uses only Linux servers. So, what happens if somone finally manages to develop a really nasty and effective virus for Linux? Goodbye to my website (for a while anyway). Also goodbye to a few million other sites. I don't have anything against Linux. The same could be said about companies using only Windows on their desktop machines.
I don't know what the ideal solution to reliability is. Obviously using multiple redundant mirror servers with different OS's is costly and possibly tricky to implement. But you get the picture....the diverse will survive. In my opinion.