Branin Johnson sent in this tip relating to the PDF Services in the print dialog box. He writes:

The Save to Web Receipts option in the print dialog box overwrites other documents with the same website name. There is an easy way around it however, there is an automator action controlling this function.

Save PDF to Web Receipts Folder.workflow is located in the /Library/PDF Services folder of the root of the hard drive. I added two lines to this file that would append the date and time to the filename. Now, pdf files of websites with the same site title, will have unique files in the web receipts folder.

You can easily modify all of the scripts in that folder to add additional functionality to your print dialog boxes.

Here's the modified file: http://www.braninjohnson.com/downloads/Save PDF to Web Receipts Folder.workflow.zip

The automator workflows are stored in the Library at the root level of your hard drive, not in your individual user library. As a result, this will change the way the web receipts function works for all users on your mac, and will require a administrator password to change. As usual I recommend creating a backup copy of the old file before you replace it with anything, just incase everything goes pear-shaped.