This is not so much a hint as it is a bug in Safari. When you option click a link in Safari, the browser starts to download that link. I use this well-known method to download images from my family members' websites. Safari has no trouble with identical names -- if a pict01.jpg file already exists in the download folder, it simply renames the newest file to pict01-1.jpg.
However, this is not so if you use a downloads folder whose name starts with a space. In that case, Safari simply starts the download and at the end of the download, tells you the file could not be written.
Solution: don't select a download folder with a name trhat starts with a space...
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040711211514144