AMD's CPU socket for desktop computers has been redesigned, with the introduction of the new AM2 motherboard chipset, which will become the single standard for all of AMD's Athlon and Sempron based desktop PCs (servers will be different.)
Utilising a similar architecture to the current socket 939, AM2 is to offer several new improvements. It will introduce a 940 pin socket design that can utilise faster DDR2 memory (up to 800MHz memory when paired with compatible Athlon 64 X2 and Athlon FX CPUs) and Nvidia's latest Nforce 5 chipset. The first processor to take advantage of this new socket will be AMDs high-end dual-core Athlon 64 FX-62, which is also being released today along with the Athlon 64 X2 5000+.
Naturally, since AM2 is a new design, you will require a new motherboard to upgrade to AMD's Athlon 64 FX-62. Upgrading to FX-62 will give you a 2.8GHz core clock frequency, as well as a pleasing 2MB for each L2 cache.
All in all, Anandtech sums it up really well in a few words "Same Performance, Faster Memory, Lower Power". Other articles/reviews are available as well: TechReport, HotHardware, and ChileHardware (spanish).