FYI, one major website which relies on subjectAltName which many of you will be aware of is github. The CommonName is ".github.com" which means it wouldn't be valid for https://github.com/, but they also have "github.com" in the subjectAltName field.

https://www.cacert.org/ also lets you generate certificates for multiple domains using subjectAltName. My website at https://secure.grepular.com/ has a CN of ".cardwellit.com", but then has three values in subjectAltName, "cardwellit.com", "grepular.com" and "*.grepular.com"