This doesn't answer your question with regards to devices, but for screenshots involving browsers, I believe that Screely is the best/fastest/easiest thing out there to use.
On this note, the worst offender in my opinion is Voyager for Laravel [1], where the "play" button has been put over a screenshot of the product, but when you click on it there's a 90 second video of a guy talking about the product. So. frustrating.