YES, get a MacAir - totally worth the investment!!! Light as a feather, saves your back. Except you still need a bag big enough to accommodate it, which is where my challenge comes in, because I also want something fashionable & stylish, but it can't overwhelm my 5'0 frame. And most of the bags in this category seem to be awfully heavy - heavy leather & hardware - heavy with nothing in it -- which seems to defeat the whole purpose. Sigh.
I have two laptops, the MacAir (for personal) and the MacPro (for work). I didn't have a choice for work (well, the choice was MacPro or clunky PC). The MacPro is still way lighter than a PC, but if you happen to have a choice, go with the Air - I cannot see any advantage to the Pro, unless you are in graphic design.
Otherwise, I am using a nylon laptop bag that is pretty boring and simple but functional and meets my needs. It has a sleeve that allows me to put the bag over the handles of my carryon or luggage, which is KEY requirement for me in a laptop bag, since I travel a lot for business. It is way bigger than I need for my MacPro, so I stuff all kinds of things in it, clutch bag, scarf, sweater, flatiron, quart size bags with liquids, book/magazine, etc, etc...
If I am not traveling, but just driving into the office for the day, I just hand carry my laptop in a neoprene sleeve. I work from home so in-office days like that are rare, maybe once every few months. When I worked in an office and had to walk a lot around the campus, I used a serviceable/not fashionable laptop bag on wheels -- to save my back. Those PC's are so heavy.
Go for the MAC! Your back will thank you!!