Particularly since right now comment emails are not being sent consistently. The unofficial word is that this problem may be fundamentally unfixable, though people are trying.
Things to note:
- It's kind of limited for free users (only ten most recent comments).
- It lists only comments you've made and comments in your own journal. There's a view held among the senior geeks that being able to get a list of anyone else's comments is a privacy violation, even if the individual comments are public anyway. So it's almost certainly not going to be extended into a really useful feature of aggregating comments from any user you're interested in.
- There may one day be a feature that would allow you to get a notification whenever anything updates that you're interested in, but that's very much in the pipeline and at a 'don't hold your breath' level of development.