I wrote a post on Inside Aperture titled, Plug-Ins Same as External Editor? I Don't Think So, where I disagreed with some folks on the web who say that Aperture's plug-in architecture is no different than using an external editor in Lightroom. Personally, I think there are differences, and pointed to an article by Micah Walter that does a good job of listing them. But some readers disagreed. And what followed in the comments is an interesting debate about Aperture, Lightroom, and sometimes even Photoshop. I thought you might want to take a look and decide for yourself.