Allow me to specify site in the url, such as "http://pdfmyurl.com&site=cnn.com" --bookmarkable!
For sites I regularly want to visit in .pdf form, it would be great if I could specify the site in the url. For example, http://pdfmyurl.com&site=cnn.com would take me to the pdfurl.com page and immediately perform the conversion on cnn.com.

The syntax for what your looking for is:
http://pdfmyurl.com?url=cnn.com
Take a look at the advanced options by clicking on the advanced link on the home page.
You might also want to drag the bookmarklet to your bookmarks bar, or in internet explorer you need to right click and add to your favorites.
The bookmarklet is basically a script that does the above with one click.
Let us know if this is what you are looking for?