Just read a introduction on the change of Offline file in Vista from Navjot Virk, program manager for Offline Files in Windows Vista. I feel it is great and would like to share with yours:
Offline Files in Windows Vista offer much improved synchronization. The improvements to synchronization are two-fold. First, Offline Files in Windows Vista uses a new faster algorithm to determine what files or directories are different between the client and the server. Second, Offline Files in Windows Vista uses “Bitmap Differential Transfer” when synchronizing changes from the client to the server. Bitmap Differential Transfer is essentially a mechanism to keep track of what blocks of file were modified when offline. When synchronizing changes from the client to the server, Offline Files in Windows Vista sends only those blocks of the file that were modified offline. In Windows XP, Offline Files always copies the entire file even if only a small part of the file was modified.
Bitmap Differential Transfer makes the synchronization in Windows Vista more efficient and enables Offline Files to cache large files like .pst and .mdb files. Because Offline Files in Windows XP could not synchronize large files efficiently, files like .pst and .mdb were by default not cached. Offline Files in Windows Vista can cache all file types and by default no file types are excluded.
Please note that the Bitmap Differential Transfer in only used when pushing changes from the client to the server. This optimization is not used when pulling changes from the server to the client. If a file is modified on the server when offline, Offline Files in Windows Vista will still copy the whole file down to the client during synchronization. The impact of this will be more pronounced for those users who modify the same files from multiple client computers.
Also, note that Bitmap Differential Transfer only works for pre-existing files that are modified in place. Bitmap Differential Transfer will not happen for files that are created while offline. Some applications, like Microsoft Word, do not modify the file in place. These applications create a new temporary file with the changes and later rename the temporary file to the original file. Bitmap Differential Transfer will not happen for such files.
All improvements to synchronization including Bitmap Differential Transfer will be available against any SMB server, for example, Windows 2000, Windows 2003, Windows R2, NetAPP server, etc.
Offline Files in Windows Vista also provides per-user synchronization. All synchronization operations only synchronize files that the currently logged on user has access to. Offline Files in Windows XP would always try to synchronize all files in the cache including files that where cached by other users. The logged on user would see synchronization failures for the files that he did not have access to. In Windows Vista, the user will only synchronize his files (files that he has access to) therefore he will never see errors for files that belong to some other users (files that he does not have access to).
Also, synchronization of Offline Files in Windows Vista can be scripted using WMI.