This is probably one of my favorite ideas. It's something I try to remind myself regularly, but I do think it needs to be paired with another philosophy: This too shall pass.
However, understanding the idea the now is life -- that's the key for peace and acceptance, I think. It's interesting, because my kiddos are both good at living life in the now. However, they need the reminder that whatever they're experience now will pass -- D because he's so pessimistic, and E because she gets bored so easily.
For adults, I think it's the other way around. We need the constant awareness that life is right now...we tend to think ahead (or behind) rather than simply breathing in now.
What do you think?