Anything Google does to prevent my needing to dive into my email to perform simple tasks gets a big old thumbs up, which is why I'm stoked (*STOKED*) that Gmail is getting a new set of "quick action" buttons that'll let you do more directly from your inbox subject lines, without actually opening up an email.
Ultimately, it's up to the developers of services to build this type of functionality into the emails they send you, but Google does provide a few examples of the changes you can expect:
Seamless and even modify OpenTable reservations—all without opening an email. And for the deal lovers out there, you can conveniently save a promotion from Google Offers with one click, making it easy to find and buy it when you're ready.
Additionally, Gmail will also have new buttons that will allow you to instantly view uploaded videos on YouTube or Vimeo, or view documents in a Dropbox folder or Google Docs. Yes, yes, Google. More of this. [Google]