I agree that for you it's 3 more clicks, but for the millions of other regular users, it's less useless info on the way.

People have to get that it's a product for many, not for all. You can agree with hiding emails or not, but a company as large as Google wouldn't hide it just for the sake of it. Obviously there was research and data that backed that change.

Bottom line is, if it was your company, you'd hide stuff to improve the experience of 90% of your customers at the cost of a few without another thought.

While that may be a good point, you also need to consider that Gmail is part of Google Apps for Business. I don't really mind the changes for my personal Gmail account since most of the emails that go through there are quite simple and these changes don't have any real impact on my workflow. But for my work account, it's a whole different story. Most of these changes make my experience quite annoying when dealing with business emails where I often need to copy email addresses, modify subjects, CC people, etc.

Breaking Gmail for business users doesn't seem like a good idea since they are the ones who are actually paying for the service.

It's an online web app. You can give different people different interfaces for the same data. You can even let them choose which interface they prefer. Your data-collection might tell you that 90% of users would be better off one way, but that's an argument for changing the defaults, not for alienating a chunk of your userbase. And if every change like this is upsetting 10% of your users...

Revolutionary idea! Why not use Thunderbird?

Or any other mail client?

Nobody wants to use Thunderbird just because it's faster than using the web interface, more functional, adds useful features, and keeps a backup of your email on your hard drive.

Unfortunately it involves running a program on a PC and the PC is dead. Nobody uses PCs any more. Didn't you get the memo? :-)