I carry around my Alienware 18 all the time.
Why a gigantic gaming notebook with a 18 inch screen that weighs 12 pounds?
I get a discount via my own side business from Dell, so I got a good deal. And its one of the only laptops powerful enough to handle some of the software I use, and I can use it on the go, as much as I like the rMBP, it just wouldn't be enough.
I use the carrying case that Alienware gives you, its got regular handles and a shoulder strap, and room for any papers, folders or external batteries that you might need. I also keep an iPad air in the same bag.
I find it very portable, still fits on any table just fine, and I wouldn't call it an ultra portable tho.
Hopefully that helps, if I can handle carrying around a 12 pound 18 inch laptop, you should be able to handle a 15 inch 5 pound laptop with no issue.
It always blows me away that someone would call a cMBP " heavy ", I mean how weak are are some people? Hit the gym. My clamshell iBook I had my senior year of high school would break these folk's arms off
