To be alive, working on my product, in this day and age. Because, let's face it: for many of us working on companies and products right now, we wouldn't be able to do what we're doing at any other point in human and technological history. Cloud and mobile based infrastructure is, when you think about it, very young. And it wouldn't have been possible years or decades ago because companies like Google didn't exist then (and I think we're all grateful to have you guys around).
What a wonderful, interesting time to be alive.