A third heavier, and it really feels heavy for its size. It's one of the things that made me decide not to get a Mac. I don't know why they use so much aluminum.
They are super sturdy. It's a single piece of metal that is carved into shape. And aluminium is also very easy to recycle.
I personally preferred the design of the first gen retina Macbook Pro. It felt so sleek and thin. The current design is a bit too chunky and boxy for my taste.
If we're talking æsthetics, I find they all look like silver blimps (glad they're finally shipping darker tones, but it's an affectation). I've seen a lot of dented Macbooks. I don't think they're any sturdier than any other well built laptop, which last until they're obsolete (5 - 10 years). The alu does act as a heat sink, but I doubt it's necessary for the entire body.
I'm sticking with Thinkpads for now, I like the function-dictates brutality of their design and I think carbon/magnesium and some plastic is a good approach for a much lighter result. A Macbook Pro is not only heavy, but slippery. A lot of carbon is used recycling and even shipping aluminum, and the decreasing factor of being able to easily upgrade/repair components. I don't know ultimately what the environmental impact is between the materials, but Apple has advantages of consistency and scale; as much as I like Thinkpads, I don't like that there are a dozen different models each year, which would be impossible to effectively recycle even if they had a program in place.
We're pretty much into a blog here (here's a picture of a beach), but I tried a Macbook, had to return it because of ergonomic factors including weight; I got a pretty great 16" Thinkpad with the same weight as the 14" MBP, I don't even want to think about the weight of the 16" MBP. It's frustrating other top tier companies or the industry can't find a way to have efficient product cycles (Framework is getting there). I guess it doesn't help that Apple has patented their unibody design, which shows how much they care about environment in the larger sense.
Wait for the more power hungry SKUs. Their previous gen supported up to 96 GB of ram on the higher end SKUs.