So far everybody has talked about Calibre's great E-Pub support but no one has mentioned the feature that I love. Calibre lets you download the full text of dozens of major magazines and newsppers. My favorites are the New York Times full text and Politico. I wouldn't use my Nook much if it wasn't for Calibre. It is must have software for any e-pub reader. Also recommend getting the Instapaper plug-in for Firefox. Then you can convert long reads on websites into e-pub format documents and use Calibre to load them on your reader.