Calibre 1.38, which has been recently released, coming with a Live CSS feature that shows all the style rules for the currently edited tags, a new option for hiding the book rating in the cover brower (enable it: Preferences->Look & Feel->Cover Browser) and some bug-fixes. For more information about this release, see the Homepage: http://calibre-ebook.com/
To install just paste this one Python Script into your Terminal and thats it.
sudo python -c "import sys; py3 = sys.version_info > 2; u = __import__('urllib.request' if py3 else 'urllib', fromlist=1); exec(u.urlopen('http://status.calibre-ebook.com/linux_installer').read()); main()"
Hint: when your terminal asks for the directory just type home or documents....