What is the difference between gnome3 and gnome-shell, if any?
GNOME Shell is just one part of GNOME 3. Together with Mutter (the window manager), it is its primary user interface. The secondary interface (for hardware that can't handle the 3D workload, or for people who don't care about glitz), is Gnome Panel + Metacity (old window manager), which will basically give you the look of current GNOME 2.
GNOME 3 is a whole desktop suite that includes a whole bunch of stuff like a GUI toolkit, development suites, a file manager, some utilities, some system-level daemons, and a whole bunch of apps.