cool. Just remember, all zero degree bags are not created equal. And usually zero degree bags mean you'll survive at zero degrees, not be warm.
I'd recommend talking to Mesha on here before buying one. I'm a fan of down but synthetic bags have lots of great properties as well. I slept in my marmot down bag last weekend under the stars in 20* weather and I was toasty. But that had a lot to do with my pad as well.
I would suggest to those who may be cold as well since no-one is backpacking in to bring an extra Nalgine bottle and fill it full of boiling water and toss it in your sleeping bag... start off the night with a nice hot sleeping bag and it can keep you warm for hours and hours