In KDE, file transfers (copy and move) write to a .part file (foo.bar becomes foo.bar.part).  When the transfer is completed, the .part extension is removed.  KDE (and maybe Thunar and Firefox as well?) uses the .part extension to determine if there is a partial transfer that could be resumed.
Nautilus doesn't seem to add this .part extension, which leads to the following issues, which are annoying especially when transferring large files, or files over a slow connection through sftp/gnome vfs:

1) If a transfer fails due to some error, Nautilus may leave behind the partially transferred file in the destination folder.  However, retrying the transfer will remove the partial file and start over from scratch.  If I cancel the transfer (say I need to turn off my laptop), the currently transferred part gets deleted, forcing me to start over.

2) If I am copying multiple files from multiple folders, and the transfer dies, it can be difficult to find partially transferred file that Nautilus as trying to copy before it stopped.  The .part extension would make it obvious for me that a file is incomplete.

Implementation:
When transferring a file from /a/foo.bar to /b/, nautilus should write to /b/foo.bar.part. and then remove the .part extension when finished, just like KDE.  This should happen not only with local file systems, but also over SFTP, FTP, etc. From what little I know about GNOME, the vfs makes this transparent, so I'm guessing that this can't be that difficult to implement.  Maybe a magic number could be added, along with the original file size so Nautilus an be extra sure that it can overwrite the .part file.

I have some programming experience, but none with GNOME, so if someone pointed me to where to look I could mess around with the source and maybe submit some code or a patch...