Pros:
We can see users' avatars in their comments.
Cons:
We have recommendations appear in the same place our subscribed user activity appears in, which I really hate.
We need to go into our inbox to check if we have new messages, instead of just looking on the main page.
Just today, I saw a normal comment on a video, and the next comment I saw said "ponycigarette", because of the previous commentor's pony avatar.