You can use Firebug/Web Inspector to adjust your layouts in real-time without needing to go back, modify code in your editor, save, and reload the page. There are some new tools (backfire) out that will even let Firebug/Web Inspector automatically update your CSS file so you don't have to go back after tweaking it in browser. Hopefully, browser vendors will one day bake this functionality in to their browsers.
The biggest time sink is not being able to drag and drop it's cross browser support. I can spit out a page from a design pretty quick, but getting it to look consistent across four or five different browsers takes forever.