UX: "Interactions" is just "Notifications" but less cramped
The Notifications panel more or less feels like a more cramped version of the Interactions screen.
Benefit: Convenient access to see and interact with events that pertain to you. For a person who isn't easily distracted, this is good.
Drawback: It makes the UI look too busy, whick can be overwhelming for a new user (such as me currently). For someone who's trying to reduce distractions (such as yours truly), the extra timeline isn't good. Also, I find myself dithering between using one or the other, which adds mental overhead.
This is basically a hybrid between a TweetDeck type interface and a Facebook type interface. I imagine that the intent is to have the benefits of both, but it feels more like the UI can't make up its mind about what it wants to be.