I have both IPAD 2 and 2011 MBA 13. I had IPAD 1 and MBA 2010 as well. The longer I own both the more I use the MBA over the IPAD. With the IPAD I end up not being able to do as many things so I have gotten to where I just pickup the MBA the 1st time.
I use the MBA 80% of the time and use the IPAD when I am just browsing in bed.
Surprisingly enough, I have found that I really enjoy the IPAD 2 for taking pictures (and sharing them) in my business.