A small tweak in Twitter's default settings has many users up in arms. Most newbies will probably not even know what all the fuss is about.
Before the recent change, the default setting for what you could see included tweets between two people if you were already following both of them, but not if you were just following one of them. However, Twitter did include the option of changing this default to allow users to see all the correspondence sent out by those they were following. For many, this was too much stream of consciousness, but others enjoyed watching a whole debate develop. This latter option has been removed!
What this also does is remove the more serendipitous nature of finding people with common interests and views. It is often the case that seeing a reply from A to B - where you're following A - will lead to looking at B's profile and possibly thereby following B as well. The new changes mean this will happen less. The full feed is available if one goes to A's user profile or the global timeline, but that isn't the best way of using Twitter.
Nobody seems entirely sure why Twitter has done this. Bandwidth problems?! But the Twitter management is now finding their communication tool being directed at them.