The #1 feature I'd like to see for Lightroom - the addition of dynamic and customizable buttons that will act as a drag and drop source for resizing the current picture to an arbitrary size/format for emailing/copying/uploading. (i.e.: if you drag from the 800x600 jpeg button, you get an 800x600 version of the current image to drop somewhere, without having to explicitly save the file to disk first or clean it up later). The temporary files should just be deleted when you quit Lightroom.