Business Computing World published a review of Apple's Mac Mini Server

For small businesses where Apple Mac is the predominant desktop the Mac mini with Snow Leopard server makes a lot of sense. It's small and very efficient, and provides most of the file sharing, workgroup collaboration and other services such companies need. It's also easy to manage and in such situations a cheaper and better alternative to a Windows server. As the number of Windows desktops increases, however, a Windows server starts to make more sense and we can't see many all-Windows networks opting for the Mac mini instead. Scalability could be an issue on larger networks too, and in companies where large amounts of data need to be stored and shared a NAS appliance could be a better choice. Yes it's small and looks cool, but bear in mind that a lot of what you can do with the Mac mini server can also be done via hosted services. These, typically, cost less, are even easier to manage and, with the server hardware located elsewhere, take up no space at all.

  Apple Mac Mini Server Review