If you're sharing your apps with customers for very benign purposes, I doubt they'd care. For instance, if you were giving customers access to your business's data or some sort of internal app that provides functionality that you wouldn't want to make public. That seems very reasonable, and might not even be outside the ToS (IANAL, and I haven't read them).
In both Google and Facebook's cases, they were using it to distribute apps to the public at large (i.e., users with whom they have no business relationship) simply because they couldn't get the apps into the app store to begin with because they would otherwise violate Apple's rules. So not only were they flagrantly disregarding the ToS of their enterprise certs, they were doing so in order to violate Apple's rules for app distribution. Less than great.
In both Google and Facebook's cases, they were using it to distribute apps to the public at large (i.e., users with whom they have no business relationship) simply because they couldn't get the apps into the app store to begin with because they would otherwise violate Apple's rules. So not only were they flagrantly disregarding the ToS of their enterprise certs, they were doing so in order to violate Apple's rules for app distribution. Less than great.