UEFI (Unified Extensible Firmware Interface) is a standard designed to replace the venerable PC BIOS. It is hosted by the UEFI Forum. Plans and specifications for UEFI have been in the works for years and the work has been supported by a wide range of vendors including Intel. Intel's delivery of Sandy Bridge (see An Embedded Sandy Bridge) is the tipping point for most motherboard vendors. This was a major motherboard design change and adding UEFI to the mix makes sense.
The other reason for the move to UEFI is to overcome many of the disk limitations that are now cropping up as drive capacity increases. Without getting into too much detail, the master boot record (MBR) used with most hard drives has a 2.2 Tbyte limitation. Booting from a very large disk partition is also an issue. Seagate's latest 3 Tbyte hard drive actually includes special software to allow older operating systems like Window XP to handle the drive.
UEFI handles drives larger than 2.2 Tbytes and supports the GUID Partition Table (GPT). GPT replaces the MBR allowing larger partitions and the ability to boot from any of these partitions. Drive capacity is one thing UEFI addresses.