I often find myself sending PDFs of web pages over email, but have always used the “Save as PDF” function selected from the printing dialog box. I accidentally discovered that if you press Command-I while in Safari under Tiger or Leopard, Mail will open up and attach that web page in HTML format. If you press command-shift-I, Mail will open up and add just the URL to the message.
Because OS X is designed with shared resources called Frameworks, Mail calls on the same underpinnings as Safari. For this reason, you may notice that Mail is extremely competent and quick at rendering web pages.