Feature: The new Finder
How it works: People have been complaining about the Finder since OS X was first released. Finally, Leopard brings a variety of long-awaited features. Perhaps most important is the one-two punch Quick Look and Cover Flow, but there are a many other new features as well. The new Finder takes its design cues from iTunes, with the sidebar now looking very much just like the source list. Taking a cue from Cocoatech's Path Finder, Leopard adds a live path bar to the bottom of the Finder windows. There are also new folder view settings and the option to make particular folders sharable.
Who will use it: Everyone, and while it's unlikely all the critics will be fully satisfied, the improvements will likely make third-party Finder replacements seem less necessary.