I'd be curious to see what the opt-out rate on the new compose UI was. I like to adopt new UI improvements but that was one of the few that I immediately hated and switched back. I wonder if this feature was liked more or less than some of Google's other UI changes.

I get the feeling that Google is ignoring user feedback for some of these types of thing so they can push users towards their corporate goals. Youtube badgering people to switch to their Google+ username is a good example. Clearly a lot of people don't want to do that, yet they persist.