Indeed, closed loop calibration has confused quite a few users. It's an entirely different concept from actual profiling, as the new Z-series do. As Greg says, closed loop calibration returns the printer to a known state, again and again.
This merely means that if you print through a certain profile in January after calibration, the print that you will make lateron in August will look the same after a new calibration because the printer was returned to te same state.
But what if the profile you used is crap? The first print will be crap, and the second print will also be crap. They will, however, be equally crappy.
However, as I pointed out in the article about Gamutvision and PrintFIX Pro that Michael posted a few weeks ago (Fancy Graphics Galore), I don't think the canned profiles from HP are crap at all, I think they're quite good. The profiles I made with PrintFIX Pro were different, not necessarily worse, not necessarily better.
I agree with Andy - it would be a good idea to have software that gives you more control over actually making and editing profiles. As I've learned from the people in Barcelona that design the HP printers, profiling is in essence a subjective process, indeed, 'part art' as Andy indicated. So let's leave the art part to the photographer. With PrintFIX Pro, you have the option to punch in some more magenta, or to reduce the cyan somewhat, but that's all very basic.
It would be nice to have the same level of control over profiling at the end user stage that for instance Adobe Camera RAW or Capture One offers in RAW conversion. That would be neat.