EndNote's main competitor Zotero's main advantage (apart from being free and improving fast) is being able to 'scrape' citations from websites saving us the effort of retyping them. But it can only do that from websites that use a certain standards (such as this site) or that were specifically encoded for Zotero. These now include CiteULike and LibraryThing which have a lot

Zotero is now compatible with LibraryThing and citeulike. Users can now capture bibliographic information from both lists of references and individual items in citeulike and information about any individual book in their LibraryThing collection.

Zotero: The Next-Generation Research Tool » Blog Archive » Better Connecting The Research and Library Web