We have had a number of customers and employees complain that they were not consistently receiving notifications for comments on Ideas.
We've discovered that it only appears to be the case because the options for notifications for Ideations/Ideas work differently than for Forums and none of us understood the "rules".
Under Account > Settings > Notifications there are two options (in the "Activity from subscriptions" section), for receiving notifications for comments or status changes on Ideas I'm subscribed to, and not Ideations I'm subscribed to.
It's (too) easy to miss the subtle difference between those two things (or not even to know about all these different notification options).
Nothing is mentioned about these Ideas notification options on the "How to receive notifications" page of the Ideation Wiki. Please add a mention and explanation of these options to this wiki page.
Also, none of these same people were able to figure out how to get notifications for any comment posted on any Idea (within an Ideation) - until it was pointed out to us that you can "subscribe" to an individual Idea (when viewing a specific Idea you scroll to the bottom of the original post and next to the date you click on More and then there is a "Turn idea status and comment notifications on/off" option).
Please also add a mention of the ability to "subscribe" to an individual Idea to this same wiki page.
On the XPP forum an explanation was posted for the benefit of the customers (and employees) who had complained about not getting (XPP) Ideas notifications: FYI: The "quirks" of notifications for Ideas pages
It might give some ideas on what to add to the wiki page.