An off-site delivery for Gmail recipients would be a big step forward. Instead of seeing an actual email, the recipient would get an https link to a page on some non-Google server. Extra bonus for attaching an explanation along the lines of "your peer decided not to share the contents of this email with Google."

What really ticks me off personally (and I fully realize I'm not in a majority here, even on HN) is sending an email to john@domain.com only to see the reply come back from Google's servers. In many cases I would've not sent the original email if I have had known it would go through them. They've got enough data on me as it is.