If you're coming from a previous ipad (especially ipad1,3,4) you'll notice a huge difference. Not only in weight, but also in width. It's much narrower in design so holding in portrait is a joy. Typing in portrait is a breeze as well.
I've used my air in bed to read and I usually hold it above my head, but with 2 hands and it's fine for me.
One-handed use is also MUCH better. You'll be able to use it one handed much like you would hold a thick magazine in your left hand (for example).
If you're coming for a mini, however, you'll notice the extra .25lbs...but it's not bad at all. Another user described holding the air as wielding a thin large notepad, and I have to agree.
Overall I'm impressed every time I pick mine up to use, because the screen is so large I feel like in my mind it should weigh much more than it really does!