I sold my Thinkpad X201s and got a Macbook Pro 15" after I got my iPad. No regrets here. As a portable companion, I think the iPad is phenomenal.
The Macbook Pro is not so bad either.
I would make the argument that even a netbook + ipad > laptop + netbook. The iPad is in a class of its own. The netbook is just a cheaper, slower, and more portable laptop.