In response to an older post CAD for the iPhone, a reader points to
SitePAD: Pocket Aided Design for your iPhone. $10 dollars is a little pricey, but could be worth it for someone who needs to see/edit drawing on the go. Also might be hard to use on the small iPhone screen. The description in iTunes says that SitePAD is compatible with the iPad, but no screenshots yet. That would be interesting - a large screen CAD application optimized for multitouch.