Aspect ratios, dots per inch, file formats and conversions, forgetting where you saved that file, these are all problems that are disrupting my creative workflow. More and more I just work with screen shots. If the image looks sharp on my big 27" monitor, I crop it as I want it, and use it in my presentation. It could have been a JPG, a PNG, a web page, a PDF document, a Keynote file, it does not matter. CMD-SHIFT-4- and “click”, done.