Apple announced late last year that it was discontinuing their server appliance, Xserve, this year. The time is near. If your company needs to upgrade its server hardware and you like the Xserve form factor then you have but a few days to order one.
There's an interesting article on Appleinsider.com about the value of the Xserve compared to Windows-based servers. The difference in cost is staggering, especially when one factors in the annual cost of the CAL, Client Access License, compared to what Apple charges for their server and software.
Here the link to the article that compares the two technologies.
The server software will still be available for the Mac Pro, but the form factor is 4U compared to 1U of the Xserve.
Erik