There's an interesting tradeoff -- marketers no longer know your location, browser, client or how many times you've opened the email. However, any spammer now instantly knows that the email address is valid.

It's probably an improvement, but not all the way there. For actual privacy, what GMail needs to do (and I realize this is slightly unfeasible due to the amount of email they receive) is instantly open and cache every single email to every single email address (including non-existent addresses).