Hicksdesign wrote a custom theme for Google Reader, influenced by the clean design of Mac applications. The theme is actually a user stylesheet that includes new icons and leaves more room for the content. It should work in Firefox, Opera, Safari, Camino, Omniweb (from the instructions, in Opera and Omniweb setting up the theme is a one-step process).
There's also a similar theme for Bloglines, the elder brother of Google Reader.
Source:? Google System
Google, Google Reader, Mac, Theme, Mac Theme