Let's say I see a very interesting question, one to which I do not the answer but would very much like to have. I see no way to "watch" that question. Is there a trick to doing this? Is this a feature we can add to this site? I would expect a blue or yellow pip in my mailbox when someone posts an answer.
You can favourite the post by clicking on the star next to it (below the voting buttons). In your profile, there will be section for these questions which will show the number of changed posts. It's manual, but one way to keep track of interesting posts.
It won't show up in your SE "mailbox", but there is an RSS feed for every question: the link is at the bottom of the page:
Subscribing will allow you to monitor updates to the page.
Yes, it is possible now!
Refer: The Follow Questions and Answers feature is now live across the Network for more information.
You can follow any question and answer (not posted by self) and you'll get notifications in your inbox upon addition of new answers, revisions and comments etc. activities (excluding activities done by self).