FYI re adding hp printers and All-in-Ones:
Add the printer using the Gnome add printer wizard or by running the
'hp-setup'. Either will auto-detect network printers, select a ppd,
and add the queue. The add printer wizard in the CUPS web interface
is way more work.
If you're adding an Officejet All-in-One, hp-setup will also setup the
fax feature.