If you want to try out Windows 8.1 preview right now, you can. Be aware that when you install Windows 8.1 preview that you will have to reinstall all your apps. If you then upgrade to the final RTM version you will have to do this again.
Going from Windows 8 to Windows 8.1 RTM does not have this reinstall requirement nonsense
You can download Windows 8.1 preview here http://windows.microsoft.com/en-us/windows-8/download-preview
To see what is new in Windows 8.1, check out the Windows 8.1 Preview Product Guide.
Here is also a video showing Windows 8.1[video:youtube:VQb5caeSo00]
Here is another video released today, this is is an ad really