Printing web to PDF

So I was just thinking to myself that I'd love a way to make web pages available offline for airplane and other types of offline reading.

Then I remembered Universal Document Converter.  I'm sure there's some free, open source thing I missed, but a while back I had to convert something to a TIF file or something random like that, because it turns out the copy of Powerpoint I had wasn't exactly kosher.  So I wound up paying for the Universal Document Converter and it's been a really easy way to print documents automatically to PDF.  I don't own a printer and try not to keep any paper files, so this has been a great way for me to organize my digital documents storage.

So I just realized I can easily print web pages to PDF and keep them for later.  There's a bunch of stuff I'd like to read on my plane ride back to NYC and now I have a bunch of PDFs in a folder.  Nice!

Still, it would be cool if something could run in the background pulling in my links that are tagged PDF and automatically do this for me.