Inbox in conversation view
One of the Gmail features many people like is the conversation view. This is the inbox view where various emails are embedded with each other to show the "conversation" of related emails. Some users love it and some, like me, don't like it at all. While the change is a subtle one, I find the conversation view confusing so I turn it off.
These screenshots were made to illustrate the steps in a Quick Tip in the Google in the Enterprise Blog.