If I like the answers posted by a user on Stack Exchange, is there a way to follow the user? like for example, set an alert so that whenever he asks a question or replies to a question, it is notified to my gmail account?
There is no internal concept of "following" a user because (all together now) this is not a social network.
However, all is not lost.
There are RSS feeds for users (and tag and question feeds). Click on the username to get to their profile page, choose the "Activity" tab, and look at the bottom left.
I don't understand the point between social network and following an user actually. Is there a commonly accepted definition for a social network ? I've gone on this reference [ http://en.wikipedia.org/wiki/Social_network ] and I found nothing about the use of email address for instance. Or I badly read this long page.
By the way, I also would like to be able to follow some other users. I propose to do that the same way it is implemented for the favourite tags for instance: we have a list somewhere (actually in the right of the screen) and we can filter the questions clicking on a specific tag. That would be enough for me. Moreover, I've the feeling this has nothing to do with a social activity.
What would be a social activity for instance would be to ask some questions to some other people, and they answer you... well, what a discussion is about, isn't it ?