What new functionality does failover clustering provide in Windows Server 2008 ?

New validation feature. With this feature, you can check that your system, storage, and network configuration is suitable for a cluster.

Support for GUID partition table (GPT) disks in cluster storage. GPT disks can have partitions larger than two terabytes and have built-in redundancy in the way partition information is stored, unlike master boot record (MBR) disks.