Great job with Acorn — it just keeps getting better!
I find myself marking up screenshots regularly, and often revert to my older version of Bloatoshop, because:
1) I don't like the (to me) goofy "Skitch" arrows, which can only be streamlined correctly when perfectly horizontal or vertical. I would love to see Acorn have arrows as a function of the line tool;
2) Editing a text layer: when I go back to a text layer, Acorn requires me to select the text box with the Move tool. In Acorn, using the more intuitive (PS) approach of using the Text tool to get back into the text box instead creates a new unwanted layer.
3) I would like to see a keyboard shortcut for opening, and check box for closing, the Inspector. I have a decent size screen, but it still gets in the way, and having to go back to the Window menu to temporarily close it is clunky.