Good stuff, OldToad. I suspect you were a batch-file wizard back in the days of DOS.
If it really is the QBO developers' intention to make all attachments (including PNGs) trigger "Save as," would it be possible with Automator to right-click an attachment that you have uploaded, and it will download the file, open it for viewing, and then delete it when you close the viewer? That would be a workaround I could live with.
On a related note, I found a keyboard shortcut trick that allows me to use Command+P+P (hold down Command while hitting the P key twice) to make printing as a PDF a bit quicker.
