Vista's New 'Copy' Dialog
Info from LonghornBlogs.com :
Some of the more useful improvements to Windows Vista come in the underlying file system. There are a ton of improvements under the hood to make files easier to deal with. One of the more subtle but important differences from Windows XP is the way discrepancies are handled during file transactions.
In Windows XP, if a file encountered some kind of error (file already exists, etc.), it was handled at the time it occurred, interrupting whatever you were doing. If the same thing happens on Windows Vista, the operation continues, and you are prompted to resolve the conflicts at the end of the process.
The UK's Official Windows Vista Magazine covers it as one of their favorite features: