How's this? I made the new posts button default to all new posts whether they are read or not like raspadoo suggested. I think that's a good idea.
If you want to see only the stuff that you haven't read, click the little unread content link just below the orange buggy (also at the bottom right corner of the site).
Would that work best? You can always create your own custom filtered stream in the Activity tab, but that custom button will be in the Activity drop down menu. Just trying to make this work for everyone. Let me know.