Framed differently: it's 37% taller and 25% heavier. In the context of laptops, this is pretty hard not to notice. I have an MBA and my wife has an MBP — the difference is very easy to see/feel.
Its not like killing you lifting a little bit more, its already so light. Its certainly appreciably much lighter than the 15 inch 2012 mac still kicking around my house. It feels easy to hold one handed even.
I wouldn't mind that much, but my petite wife sure wishes that she could swap her MBP for an MBA! She takes her laptop in purses and other bags, so it's both about size and weight.
I just lugged my work-issued MBP through a couple of airports today, and wow, I wish I had my own MBA with me instead. That weight doesn't make a huge difference on your lap. It sure makes a difference in a carryon bag.
