A. One of the features of Office 2010 and SharePoint 2010 is the use of a new protocol, MS-FSSHTTP, which facilitates synchronization of files via SOAP over the HTTP protocol. This new protocol allows locking of portions of a file, allowing the concurrent co-authoring of the same file. It also lets you download and upload only changes to an Office file, instead of the entire file (which is what occurs when using WebDAV).
A local cache of content previously accessed by Office 2010 from SharePoint 2010 is maintained, allowing only changes to the file to be downloaded on subsequent access. This local cache is managed through the Upload Center Office 2010 application, which allows you to modify cache settings as needed. This transfer of only changes to data means very efficient use of network bandwidth.
So where does BranchCache come into this discussion? BranchCache allows the sharing of data between clients that's transferred over HTTP or SMB, so that once data has been downloaded by one computer at a location it's shared with other clients at the location, reducing data sent down the wire. Because SharePoint 2010 with Office 2010 uses the MS-FSSHTTP protocol instead of normal HTTP and has its own built-in features to handle efficient use of network bandwidth, BranchCache won't be used for the SharePoint 2010/Office 2010 traffic. BranchCache is still used for other types of traffic sent over HTTP and SMB, including data accessed by previous versions of Office.