There were a couple of things that happened here: Twitter made decisions based on feedback without going out to do full validation that the issue with @replies was really an issue.
One of the things that is so magical about social media tools is the fact that the community can shape the best way to use the tools, the best ways to optimize usage, the best ways to optimize discovery and engagement within sub-communities that develop. Self-governance. Just because something isn’t working for one group, doesn’t mean everyone is having the same experience.
Over the past several months, I have built my Twitter community via discovery of like-minded individuals focused on issues of government 2.0. The change that was implemented yesterday could have potentially cut off my ability to find new Tweeps to follow. I rely on a number of different tools to discover new friends – search and hashtags being some of the primary ones. I think the feedback from the the crowd via #fixreplies and #twitterfail spoke volumes.
Lesson here: Usability 101. Understand your audience. Know how they use the tool. Understand your users needs. When introducing changes: Test. Inform. Iterate. Communicate.