Windows has supported restartable file copies for a while. CopyFileEx() has supported COPY_FILE_RESTARTABLE for a long, long time. ROBOCOPY has handled restartable file copies since Windows NT4 - maybe eight years ago? So you might think Windows Explorer would handle restartable file copies. Unfortunately, here's what you get when your connection drops for even a second:
Same problem in Vista, despite the fact that file copies take eons. In the sixth major release of an operating system, is it too much to expect that the file system GUI handle network copies, especially when the base operating system's had the capabilities for almost a decade? Robocopy, a simple console application, tells you that the connection has dropped and that it will try again in 30 seconds. How about Explorer?