New with Panther (or possibly a Safari update) is the ability to drag images from the browser right into an email to be sent. No temporary file on the Desktop. Of course you can drag images straight into other apps (Word, etc.), but Mail is where it really adds to my user experience.
Previously you had to drag to the desktop, then to the email, then remember to delete the temporary image file after the mail had been sent.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031112111834413