One thing I'm always interested in with products like this is the economics of hosting a CDN of static assets for a large base of free users. How is it that products like this, or like Font Awesome at a much larger scale, can support the needs of so many free users? I understand that some free CDNs for open-source libraries like Bootstrap operate based on in-kind donations from hosting providers, but I still wonder how the model in general stays afloat.