I'm actually thinking of getting rid of my iPad for just this reason. I have an Air and it's fantastic for casual web browsing. It's pretty good for short emails and watching movies. But, anytime I want to do something more serious or even type a longer email, I inevitably find myself getting up to grab my laptop. Doing even some simple things like typing this post are a bit of a pain on the iPad, especially if getting content from another app is involved. It's a bit better if I set it down on a table and use the landscape keyboard. But, at that point, I'd rather have the real keyboard on my MacBook anyway.
Many people tout the ultra-portability of the iPad over a laptop, and it is lighter to be sure. But, since the Air can't fit in my pocket, it is likely going into my briefcase when I take it somewhere. My MacBook fits just as well in there, even if it is a bit heavier.
I recently picked up an iPhone 6, and the bigger screen makes it a lot better for casual "on the couch" type browsing activities than were previous generations. With my laptop now 4 years old, I am seriously tempted to sell both it and my iPad and put the proceeds toward a rMBP (especially after spending a couple days with Yosemite).