Thanks for the great feedback! I'm working on clipboard integration, and hadn't considered screenshots. Would being able to save your work to a file be what you're after?

Typically when I do screenshots that need annotated, I will just add the Control key to the keyboard combo to add it to the clipboard instead of saving a file, and then paste in an email. I typically do not need to save the files, although I am sure there are others out there who would like to see file saving.

Actually I don't need a window screenshot, I need to capture the screen behind it and the annotation. Just need to mark something up, save to clipboard and paste in email.

I tested using Grab with Acetate and it works great for this. I'm working on getting the screenshot integrated, but in the meantime this might do what you want.