I searched through the FAQs to try to figure out the "Press This" button, and I found this topic and have read through the whole thing and still have no idea exactly what it does. No idea if the WordPress staff read these comments, but if they do, it really needs to be documented.
All I know is that if I'm looking at one of my WP blogs and "Press This", it takes me to a blank posting box for a different one of my WP blogs. I have absolutely no idea why anyone would find that particularly useful, nor why it would be assigned to a default button, nor why the button would be labeled "Press This" instead of something meaningful. I'm stumped!