Lines with embedded labels?
 

I'm looking for a way for a line connecting two objects to include a bit of text. Not as a note, but as part of the line. It seems like this can be approximated by dragging text onto a line, but the text doesn't rotate as the angle of the line changes. Is there any automatic way to achieve this?

Option-double-click the line to add a label (or drag text as you did), then select the label, go to the Geometry Inspector, and there are controls to make the label parallel to the line, etc.

Hope that helps,

Exactly what I needed. Thanks!

Is there a way to do the same thing using OmniGraffle on the iPad? I know how to attach a label to a line, but I can't find any control which sets the label to be parallel to the line.

The iPad doesn't have the same richness of controls to adjust labels, unfortunately. I think the best you can do is to use the Geometry popover to turn the label to match the line, but as soon as you move the line to a different angle, you've got to repeat the process.

Good news is that it does heed the adjustments you can do with the Mac app. So, assuming you have the Mac application, make a stencil with a collection of lines with labels, set the labels to be parallel to the lines, and send the stencil to your iPad. Then use the Contact Omni button to let them know that having those controls on the iPad is important to you!