Windows 8 developer edition is out & can be downloaded from here , but features provided may or may not work depends on future release. Windows 8 offers lots of new features comparing to the windows 2008 R2 . It promises less memory utilization,better throughput and much faster then previous version of OS.
Mark has great listing of windows 8 features in details http://www.minasi.com/nws1109.htm
Windows 8 offers image based login comparing to old model of entering passwords. They got normal desktop changed to MetroUI with constant dynamic updating of favorite links like Facebook, weather stats, news etc. right on the desktop. Windows 8 promises lot more to be added and improved and promise value for money.
The major enhancement is including NIC teaming software with the OS, so no more third part software required for teaming in windows 8. Windows 8 offers GUI features in core edition which can be turned on and off based on the requirements like patch installations etc.
Form active directory load of new features has been added some are like remote DCPROMO, virtualization aware domain controllers, AD Recycle Bin/Fine Grained password management is included in ADAC GUI.
In Hyper-V some improvements are replicating VM from one Hyper-V host to another Hyper-V host w/o the need of any software, VM on file server, new VHDX format which is faster and allowing size of greater than 1 TB is possible etc.
Windows 8 promise lot more with the final release. I have not tested being busy with the client project, will add more materials on Windows 8, once i test in a lab.
Till then, enjoy the Windows 8 developer edition.