PDFCreator is a free little PDF creator (duh) for Windows. It "adds" a new printer to your system to print to PDF.
I never print anything at home... Mainly because my printer is out of ink and I'm too cheap to by more. However, with PDF Creator, I can print receipts from online purchases to PDF and archive them. When I need a hard copy, I can easily print it somewhere else (*cough* *work*).
Plus, I don't have a bunch of receipts laying around that I never really need.