e.g. this on StackOverflow:

This shows change in reputation points, and any of my questions that have new answers/comments or answers that have new comments.
We're trialling CQ and I feel that this is a vital ingredient that is missing that will stop our usage from gaining the critical mass to be a success.
Without this, users have to hunt around for these things, which a lot of users won't do. They also won't read the notification e-mails as our company already drowns in automated e-mails!
I was looking at the REST API and thought that might help, but there doesn't seem to be a way of knowing when the user last visited the site so that we could develop a plugin to search for their questions/answers that have been modified since their last visit.
Any advice welcome!