The iPads superlative battery life alone gives it special status versus the 11" MBA netbook. You'll go through two full charges on that model before you'll tucker out the iPad.
The eReader apps (iBooks for epubs, Kindle app for Kindle books, Nook app, etc.) make it a pretty good eReader. I find the Nook and Kindle to be far better if ALL you want is an eReader, but the iPad is multi-format compatible, something the dedicated eReaders are not.
The ability to view movie files in anything other than MP4 gives the MBA's an edge...but even then, the 11" netbook version tends to choke on very large MKV 1080p videos unless you use something like Plex. But still....no conversion needed for most file types. You have to convert almost EVERYTHING to some custom format for the iPad.
And although there are those who claim great skill and comfort with the on-screen iPad keyboard, I hate the thing for anything other than quick replies. For real typing and real content creation, the MBA line wins.
I'm also pretty addicted to the iTunes App library of fairly cheap games and 'applets' for the iPad. I can't hardly touch any games for OSX without dropping $25-$40. I can buy 20+ games for the iPad for that price. They may not be as deep/immersive but they are no less fun and actually better fit my lifestyle as I'm seldom sitting in front of a computer playing a game for hours at a time...but I can squeeze in 10 minutes here/there on a game for the iPad easily.
They both have their strengths/weaknesses, and they don't really overlap as much as some people may think.