Jupiter is based on ubuntu maverick, luna the next update is based on ubuntu oneiric. You could call it a ubuntu remix but its not a fair statement, the whole idea is a unified os that is designed to look and feel a certain way. They have specific apps that will replace the default gnome utilities like nautilus rhythmbox etc.
Marlin - nautilus replacement
Beatbox - rhythmbox/banshee
Pantheon - gnome-terminal
Postler - evolution/thunderbird
Dexter - contacts
I'm writing this post from elementary os jupiter. Its worth a try just to get a feel of ubuntu taken apart and rebuilt with a focus on design and usability.
However dont expect things to be polished like osx, it is not. A few "features" like postler storing your password in plain text is enough to put me off using it over thunderbird but i digress.