To expand on what Jon said...
When you edit the metadata in calibre, you are not changing the actual book. You are modifying the library. Calibre only updates the book when you send it outside of calibre. Saving to disk or sending to an ereader will do this. To update the book in place, use either the "Modify ePub" plugin or the "Polish Books" function of calibre.
As to the viewer, I like it and use it when reading an epub on my laptop.
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