I like the "Like" function because it's nice to give/get feedback on things that we post from time to time. Plus, not all things that we like deserve points to be given to the author - they just need to be validated that they're good information.
Now, that we've got that, it would be nice to have a "Subscribe" function for when we see a post that is interesting and we'd like to follow, but we really don't have anything constructive to add to the conversation. Call me "Nosy" or something, but sometimes there a post or a conversation going on that I can't contribute to, but I'd like to know how the situation is solved and follow the steps that went into solving it. I really hate making "me too" type posts, just so I can get on the notification email list for future posts. A "Subscribe" function would allow me to follow the conversation quietly until I either have something of value to contribute OR until it is solved and I learn something.
Of course, this may be the dumbest idea I've ever offered up, so don't be afraid to say so. I'm very thick skinned so I will not be offended if you say so.