I touched on this in another comment and zefhous is pretty much on the money. Where I'm at we have a web-based interface for our warehouse, inventory and CSR systems. QR codes are all over the place and with our web UI's we use Charts for QR generation. This causes a bottle-neck when things are moving really fast on the floor. I haven't looked at this yet but it sounds like something we need.

I can see it being used with wkhtmltopdf (uses webkit to generate PDFs) so invoice generation or something doesn't require an external request.

From the OP: It doesn't rely on external services which go on and off, or add latency while loading.

The Google charts API doesn't provide an SSL interface - if you use it on a page served over https, you'll get a mixed content warning.

[EDIT] I was mistaken, see andrewjshults's reply.

I had installed one of the numerous QR Code extensions for Chrome (press the button and it generates a QR code of the URL to continue reading on the phone). Unfortunately, I always wanted to send the URL to my phone _after_ losing wifi contact, so the image would fail to load. I was so annoyed that I downloaded the ZXing source and learned GWT so I could compile the QREncoder to Javascript for myself. This looks like a neater and more lightweight solution.