the ipad didn't become really useful for me as more than an ereader until i started using an external keyboard (with the incase origami case too). some people don't like that and prefer to go with a full computer. that's cool. but, the ipad is less expensive than a macbook air, same weight with the keyboard, has twice the battery life, lets you do handwritten notes, and lets you read, so i pretty much never take the computer out of the house anymore.
it also has 4 times less storage and a lower resolution display.