I used to work in architecture, and I think that's where something like an iPad really shines. It was possible to have all the drawing sets on the iPad, and mark them up on the job site to send back to the office for revisions. Being able to annotate them with photographs of the site conditions and redlining as you talk with the foreman is excellent, it makes things a lot more seamless.

Yes, you weren't going to do any actual CAD work and still need a workstation in the office, but as a digital notebook, it's excellent.