If you already own a good screen, the compact Mac Mini could be for you, and will get you -- as it did me -- into the world of Mac and OS X a lot more cheaply, but less prettily, than buying an iMac. I got set up very quickly, using a Logitech wireless keyboard and an Apple Magic Mouse, plus an ordinary Dell screen and my speakers. The included video adapter makes the connection to the screen work, or you can attach to an HDMI-equipped screen or TV. If you want to use DVDs or CDs, you will need to buy an external drive and plug it into a USB port. (£25-30). My cheap Samsung DVD drive was fine.
The Mac Mini box looks great, is completely silent, but is inconvenient to use. Everything is around the back - on/off switch, four USB3 ports, line in and sound out ports, camera memory card port, etc., and I found that a USB extension hub made life easier. That line in port will not work with a normal microphone.
Performance with 4GB memory is not good enough. Using OS X Mountain Lion generally leads you to have multiple windows open and multiple applications running, so with 4GB the Mac Mini is disappointingly slow. Luckily, it is very easy to follow the supplied instructions, unclip the 4GB and put in two new memory modules. I installed 16GB (about £100) and performance was transformed for the better. Having checked memory usage, I would expect 8GB also to give good performance.
If, like me, you need to use PC software that has no equivalent on Mac, then I would recommend the Parallels software that lets you run Windows on the Mac Mini.