Apple has released two updates for OS X Server this week in quick succession, with 2.1 bringing in some new features while 2.1.1 presumably brings in bug fixes that weren’t in the previous version.
The full list of new features in 2.1:
• managing DHCP service from within the Server application
• iOS 6 device management support in Profile Manager
• using the Server application to create a large number of users or groups
• authenticating with Calendar Server when using an Active Directory account
• renewing certificates for use with the Apple Push Notification Service
• configuring DNS entries with second level domains and aliases
• retaining network, DNS and PHP settings installing or upgrading OS X Server
• migrating from Lion Server and Snow Leopard Server
As mentioned, the feature list of 2.1.1 hasn’t changed, but presumably bug fixes were added.
It is highly recommended that you update if you use a Mac as a server machine, as it will add extra security as well as support for iOS 6 devices. You can do so via the Mac App Store here.