Apparently Google Reader (and receiving your most-read blog posts using that feed option) is gone, which a lot of people won't be happy about. The news came to me from Copyblogger, which I receive via email.
So I have taken the RSS feed widget off this blog, and replaced it with the "subscribe by Email" widget - it just means the posts from here will come to you via email rather than you reading them in your (no longer existing) Reader. If you really want to continue with RSS, the hot app for reading blogs now is Feedly. The information I have says you can move everything across from Google Reader to Feedly by using the same log in.
Over to you. Hope you'll stick with me!