Erica Sadun from TUAW gives a nice summary of the iPad vs. MacBook Air conundrum people find themselves in these days:
The iPad and MacBook Air belong to separate families, and yet they’re often put up against each other for purchasing decisions, especially when considering the 11-inch entry MBA. Both provide mobile on-the-go solutions. Both are lightweight. Both are affordable. So why go for one over the other? It all comes down to use case.
She does a great job of breaking down the pros and cons of each. She doesn’t necessarily pick one over the other, but instead suggests that you find what fits your workflow best. That is why I ultimately went with the MacBook Air and remain happy about it. I feel like it fits my workflow better than an iPad would have.