We have now, certainly, and now is amazing. But we have the past, too; at least for a while (dementia and all sorts of other things can rob us of the past). We have the future, too (though we can be robbed of that).
I live for all three. The past is where I draw from to inform my present actions; the present is where I enjoy myself and prepare for the future; the future is where we're all heading.
If I lived for the now, I wouldn't be going to college. I wouldn't be planning to study for a PhD in Neuroscience and researching assistive brain/spine implants. I wouldn't study programming languages and designs. I wouldn't be reading The Intelligent Investor. In fact, if you lived for the now, you'd probably be living in a soma-induced haze à la Huxley's Brave New World: it'd be the optimal choice, in fact. Pure neurochemical bliss.
The argument that you should live for now because you could be dead at any second is obscene, to me: it's more likely that you live than you die, and you're likely to be consistently happier now and in the future if you act like you'll be alive in the future. Evidence: planning for retirement. Seriously.
So live for yourself, sure, but live for all of yourself. Think of yourself as a smudge on a timeline: not in one place, not just in the past, not just in the future. Optimize the smudge.