It's really just Spotlight on crack. Once you've done your initial search and the file/app/whatever is highlighted, you can then proceed to instantly perform actions or scripts on it. It's basically just a really nice macro feature baked into Spotlight with a new UI.
Alfred goes a step further with a built-in keyboard-based file browser, web/custom/fallback searches, email, iTunes, clipboard, Terminal, and System integration, and best of all extensions. I can't imagine using OS X without it.
