Not exactly what you described, but I'm a big fan of Grafio for iPad as a diagram tool, because 'sketching' is the primary input. You can't import something fro

Not exactly what you described, but I'm a big fan of Grafio for iPad as a diagram tool, because 'sketching' is the primary input. You can't import something from paper, but if you've got an iPad around, you can draw on it like paper, and it'll give you the neater & better aligned counterparts of the things as you draw them. Much better than pulling shapes out of a toolbox. Or typing.