Is there a tool to aid positioning of position: absolute elements? Possibly a JS bookmarklet. It should do this and nothing else; it shouldn’t touch the HTML.
Storage could be achieved by outputting the generated CSS in a textarea.
Also it would be nice if it had features like “snap to edges” and “alignment guides”, to easily align elements to each other.
Edit: It should aid positioning with drag-n-drop.
Not exactly what you want, these bookmarklets can help you align elements on the page.
http://www.sprymedia.co.uk/article/Rule
http://www.sprymedia.co.uk/article/Unit