Currently, you can like and RT posts from Twitter in the priority inbox, but for Facebook. Meaning you have to go and find the comments in a separate Facebook stream before you can do this, then go back to the priority inbox to archive. 

When click reply to a Facebook comment in Priority Inbox it jumps down to to put your comment at the very end of a comment stream, not as a direct reply to that specific comment (like you can do in the Facebook service stream). It would be helpful if these services could be added to the Facebook comments on the priority inbox.