I've been using Google Reader more and more. I'm not thrilled with the layout, so I was really pleased to see that I could modify it either using the Stylish FireFox Extension or via Greasemonkey Google Reader Optimized
I started out with Stylish but am trying to cut down on the number of extensions I have. Of course, whether it's better to have it as a Greasemonkey script seems more open to problems than an extension. You're one level away from the scripts and they don't go through the official Mozilla check-in process.