Disclaimer: I haven't used the new MacBook. I hope to eventually make a trip to the Apple store to see one but for now I will just make some remarks about it as a Mac user.
I love the concept. The new MacBook is meant to be a mid-size computer with a retina screen, great battery life, and an incredibly thin profile. Personally this would be great for me. I would love to be mobile with my 13" retina MacBook Pro. I certianly can be but it's far more cumbersome than I would like it to be.
A good review of the new MacBook comes from Dieter Bohn of The Verge. He had some interesting thoughts about it.
This new MacBook is the future. All laptops are going to be like this someday: with ridiculously good screens, no fans, lasting all day. Just like the original MacBook Air defined a generation of competitors, this new MacBook will do the same. It, or something inspired by it, is what you'll be using in two or three years. It's that good.
My currnet Mac is fairly new, but already I think the new MacBook is likely to be my next computer. Not this year, probably not next year, and (if my Pro holds up) not even the year after that.
I think the new MacBook is the future. Eventually, I will need a new laptop. And it's probably my future computer.