Microsoft executives announced today that starting tomorrow, they'll make available via the Windows Store significant updates to the Mail, People, and Calendar apps 

Mail app get updates like the ability to create and delete folders and the ability to search for mail on the server, among others. Supposedly performance of all three apps is improved, even on low-power Surface RT devices

About the other "core" Windows 8 and Windows RT apps like Xbox Music,

according to a sources, who mentioned the coming March core-app updates, Xbox Music and the Bing AppEx applications were supposedly going to be refreshed this month, too.