A few people have asked questions about how to configure Discourse notifications, and I haven’t been able to answer well because I’ve been too busy on main site bugs to explore Discourse much. So I want to share a bit of what I do know, and encourage those who are more familiar with Discourse like @jzw to chime in with answers to questions that others post here.
First off, some terminology. Categories are the major collections in Discourse, and there are only a few here right now: #comments, #site-feedback, and #tidbits-talk. (If you type a # sign, Discourse gives you a list from which it will auto-complete and make the resulting text into a live link.) You can see and select from a list of categories in the gray box at the top. (Clearly, I need to add a description for the Article Comments category.)
Categories contain topics, which correspond to a thread in a mailing list — a single subject and all the posts under it should be on that topic. (One super welcome feature for my inner compulsive is the fact that I can move topics to different categories, and move posts to different topics.) So, categories contain topics and topics contain posts. Got it?
By default, Discourse likes you to visit the site, and it keeps track of what you’ve read and what’s new to you. It gives you a summary everything you’ve done and notifications on categories and topics you’re watching (more on that in a minute) if you click your avatar in the upper right. Also, as you’re reading, it mentions that there are new topics and replies to existing topics in a line at the bottom of the screen. It also shows you a list of those topics; if a topic is bold, it has new traffic; if it’s grey, you’ve read it all.
Categories have five options: Watching, Tracking, Watching First Post, Normal, and Muted. I won’t reiterate what the screenshot says but will just note that you get to this dialog by clicking the exclamation point button in the upper-right when you’re looking at a category.
Topics have four of the same five categories: Watching, Tracking, Normal, and Muted. Again, you get to this dialog by clicking the blue exclamation point button, but it’s at the bottom of the topic’s timeline on the right now.
Needless to say, although it’s fine to change the settings for each category, since there are only three, you don’t necessarily want to twiddle these settings manually for every topic. Discourse knows that, so in Preferences > Notifications, you can set a bunch of options that define when topics are new, when you should start tracking topic you enter, if you should watch or track topics you post in, and if you want notifications when your posts are liked. You can even enable desktop notifications, which is probably too much for most people. 
Go down to Preferences > Notifications > Categories and you can set what you want to happen to all topics in particular categories. I need to see everything at this point, so I’m watching all categories (including some private ones that aren’t yet in use internally). I don’t really have a feel for what the difference between watching and tracking will be like. Try watching a category and see if it’s annoying. If so, knock it down to tracking. And if that’s still more notification than you want, go down to normal.
Email is where it gets really complicated. Go to Preferences > Emails. There are a ton of options here, and again, I don’t really know what’s best for any given person. You might start with a lot of the checkboxes selected and then uncheck them if the email seems excessive. Note the Activity Summar, @aliamm — it may be as close as you can get to a Mailman-style digest. If you select Mailing List Mode, I think you’ll get an email for every post in watched categories.
OK, so that’s roughly what I know now. Questions and comments?
cheers… -Adam