One of the niceties of Lightroom 3 (and maybe older versions, I don’t know): a Dock-icon progress bar to indicate the progress of long import/export operations and an optional sound alert (ding!) when they’re done.
After using the Lightroom 3 beta for a few weeks, I’m sold. It’s much faster, more stable (even in beta), more polished, and more robust than Aperture. Apple should consider its ass thoroughly kicked on this one.