It works as a citation manager, but also as a really comprehensive bookmarking system. A few of its virtues: you can archive PDFs and Web pages, you can share collections of research sources with others (great for collaborative projects), export nice looking reports of resources, and import/manage citations in Word.
It can pull details out of just about anything- PubMed, Amazon, newspapers, google books, to name a few. Obviously, I am just learning about this, but have downloaded the extension to start using while I pull research, cull resources for requests, and find items of interest as I browse. I already want to upgrade to the new Beta version! Zotero has really good documentation on their website, so I'm confident I can find my way around.
Happy citing!