This came up today in response to a support question, and it's a neat trick that I think more folks should know about: In Acorn 7 you can use the Selection ▸ Make Shape from Selection menu item to convert the current selection into a shape, which you can then add a stroke to, or fill, or do whatever you want. You can even add or subtract from the selection using the various keyboard modifiers and make complex shapes from it.

The one exception to this is that it won't work with the bitmap selection tools like magic wand, quick mask, and "Make Selection from Layer". (That'll destroy the fancy math Acorn uses to keep the selection vectors in memory).

Have fun!