In 10.5, you could bring up the Get Info window (or Inspector) for a file you downloaded with Safari, and view the URL from where you downloaded it (in the More Info section), which was useful. However, you could not copy or select the URL, and had to retype it to visit that address.

Now, in 10.6 you can now drag-select across the URL field, making it easy to copy and paste -- or you can Control-click on the selection and select Open URL from the contextual menu.