Today being RSS feed backlog-clearing day, I came across Jon Hicks' Google Reader Theme, installed the Stylish extension for Firefox, added his user style for Google Reader to Stylish, and have been wow-ed ever since. Here's a rough idea how it looks (click the thumbnail for a bigger picture):
If you're a Google Reader user like me, you'd probably like Jon's theme. I don't have to say that it does look very much better than the original Google Reader theme (oops, I said it). Amazing what a talented designer can do with user style sheets.