When overwriting files (with the same name), Nautilus displays a simple "The file already exists in "xxxx".  Replacing it will overwrite its contents." message.

When unsure whether it is OK to overwrite or not, the user has to cancel the operation once, check the files' sizes and dates to make sure he/she is keeping the desired version of the file, and only then restart the file copy/move operation again.

This multi-step procedure could be greatly simplified if Nautilus provided the necessary information (files size and date) in the warning window, so that the user can determine whether to overwrite or cancel (ie., OK if it is newer/bigger; not OK otherwise) without having to interrupt the original file operation.

Other information:
Just for reference, see how the Tracker file manager did it in BeOS:

http://www.myhaiku.org/haiku/2007-06-13_tracker-overwrite.png