Wish there were a way to know which posts and comments are new since my last visit.
It's a valid point... a filter by date range could help! Or how do you see it working?
For now, to help you partially on that... after you visit a post, its title will be colored in gray #969696 instead of white #f0f0f0 in the main feed list.
For the comment, after you visited a post and someone write in a thread you visited, a little blue icon will appear to alert you about new comment(s) under that thread. If you want to get notified, you need to subscribe to that specific post or that specific stacker (for any new comments or posts).
reply
Some thoughts on what could be cool:
  • one could 'follow' or 'subscribe' to particular posts of interest and some mechanism could be available to see a list of new comment threads for that post.
  • posts could have some useful properties, similar to how email clients manage received messages:
    • seen, read/unread, save/bookmark/star, etc
    • there could be check boxes to filter out posts based on said properties
These are just some ideas.