According to Microsoft Guru Mary Jo Foley a new update for Windows 8.1 is to be released this coming March. It apparently carries some small tweaks under the hood for better memory and storage use although some GUI changes are cited too. Read the article for yourself here:
http://www.zdnet.com/microsofts-windows-8-1-update-1-rumored-release-target-is-march-11-7000025559/
http://www.zdnet.com/microsofts-windows-8-1-update-1-rumored-release-target-is-march-11-7000025559/