I've been a heavy Bloglines user (abuser!) for almost a year now. Other users, such as Chad Everett put their free time to much more productive use than I do. Hence the Bloglines Mozilla Toolkit. This thing adds a notifier and several additional features to Mozilla and Firefox. Given the additional features that Bloglines has added recently, this is a very powerful addition to the power blogger's toolset.
Note: runs on Windows and Linux (supposedly)