One thing that is broken in most cases: email signatures. I can appreciate that they serve as a practical branding opportunity like a business card or letterhead, but no one needs to see their own in a chain of replies.

I recently converted from Outlook to Gmail and end up with email tails that consist of a stack of signatures. I'd rather easily insert a signature (easy shortcut in Outlook) in the first contact with a client than have to delete one that is automatically appended to a sequence of replies. I suppose my best bet is some tweak/add-on that allows quickly choosing a canned response?

Wish there was a concise signature format that combined fixed data pairs (Phone = 1234 5678, etc), branding chances, and a maximum size+. Then (as some mail clients or web apps do) show this info as a 'card' in a right sidebar, and stack those cards in the event that multiple people are in the conversation.

+ And automatic stripping of those "Keep it green, read on screen" messages. If someone's going to print an email, they'll print the email.