If you don't know already, Windows Server 2008 uses the same activation method as Windows Vista. With the release of Windows Vista and Windows Server 2008, Microsoft made a strategic policy decision requiring for all editions of Windows, both client and server. As part of Microsoft's Genuine Software Initiative (GSI), we have added an element of engineering, which is the Software Protection Platform (SPP) that introduced new technology for our volume licensing customers called Volume Activation 2.0 (VA 2.0). VA 2.0 allows for different types of activation and is configurable by IT Pros to automate and manage the product activation process for Windows Server 2008 and Windows Vista system licensed under volume licensing while addressing piracy and key management issues. VA 2.0 eliminates the use of product keys at the time of software installation and enables better protection and management of customer-specific product keys through new and enhanced activation management tools. (emphasis mine)

Reduced Functionality Mode will similarly be gone in Server 2008. Instead, you'll be seeing a series of nag prompts asking for keys to be entered and validated, similar to how the process went with previous server O/S's.

Be aware too that your pre-RTM copies of Server 2008 are slightly different in terms of licensing behavior than will be with the final versions. This is to be expected, but for those of us who have been using pre-release versions for a while now, the relatively easy licensing process we now see will change once we hit RTM.