Firefox/Chrome: If you're a heavy Google Reader user, you may well have dozens of articles starred and feeds organised into folders or categories. This simple userscript lets you filter all of those feeds by folder, whether the article is starred, by keyword, or by author or blog so you can quickly bookmark them or save them elsewhere.
The script works in Firefox and Chrome (if you're new to userscripts and styles, we have a guide to help), Once installed you'll see a new text box at the top of Google Reader that you can use to filter by keyword, article title, article author (which only works in expanded view) and starred items. You can also invert the filter, so you can search for things you specifically want to exclude instead of include in the results. Once you have what you want -- such as all of your starred items, for example -- you can open them individually and bookmark them, share them with yourself, or use another tool to export the articles you want to keep.
Obviously this tool isn't going to help you with new articles from your favourite blogs, or if you have thousands of starred items you want to save. However, if you're less worried about what you're going to do when Google Reader shuts down but remain irritated that your Takeout exports are missing starred items or are otherwise incomplete, the Google Reader Filter userscript can help. Thanks to Yuriy for sending in the tip!
Google Reader Filter Per Feed/Folder [Userscripts.org]