I think this is the greatest innovation in web-based email since Gmail’s own release of large mailboxes (what was it? 1 GB?). Web mail has all the benefits of a website, but offers greater contextual focus. Adding specific actions to message has been a possible with extensions and plugins for a long time, but those were traditionally added by the recipient. Giving such power to the sender is quite interesting.
Of course, there will be a variety of misuses – spam, phishing, etc – but, I’m sure there will be an even greater variety of useful functionality. Like this “Send money with Gmail” example. Here is more information on what’s possible.