It sends a mixed message to the user. It appears to be a modal dialog, but you can close it without cancelling the sync (this flies in the face of standard Windows muscle memory).
The status-bar barber pole (or throbbing thermometer) is a good way of conveying to the user: "files are in flight, but the user can continue to use the application". The sync dialog is entirely unnecessary.
p4v should also throb the taskbar item in Windows 7 to also reinforce that files are in flight. A modal-looking dialog makes users think they have to wait for the completion of the sync to continue operating p4v.