MyFonts' licensing system effectively took down our entire website recently.
We have a font licenced for some number of pageviews (250,000 or whatever), and they track that via an @import in the CSS they give you which points to a URL on a subdomain of myfonts.net. Except they changed their licensing mechanism, didn't tell their customers and broke the subdomain the @import was hitting. It didn't fail immediately, just kept trying to load for ages, and so rendering was blocked and our pages didn't load. That was pretty frustrating.
We have a font licenced for some number of pageviews (250,000 or whatever), and they track that via an @import in the CSS they give you which points to a URL on a subdomain of myfonts.net. Except they changed their licensing mechanism, didn't tell their customers and broke the subdomain the @import was hitting. It didn't fail immediately, just kept trying to load for ages, and so rendering was blocked and our pages didn't load. That was pretty frustrating.