Microsoft have just announced the Windows 8.1 Preview is now available to download! If you're running Windows 8 and want to see what the future of Windows 8 will be like, go download it.
You can find the download at http://windows.microsoft.com/en-gb/windows-8/preview. Please note that when the final version is released you may need to reinstall your applications, your user data will be safe though
Update: Seems Windows 8.1 isn't supported on all devices yet... I installed it on my Lenovo Thinkpad Tablet 2 and it has gone really slow. Found out that certain Atom-based tablets aren't supported yet as they require new graphics drivers. You can find a list of these tablets Here. If you have one of these i would wait for new drivers before updating unless you want a tablet that feels like Vista.
More information about Windows 8.1 can be found Here