I would say it depends on the individual and the set in question Nemo. Avia or Avia II can usually get someone within 5% (or better depending upon the set) of a full ISF calibration when properly used. By properly used, I mean really paying attention to the included tutorials and going from there or having a trained calibration buddy run the disc for you.
If a set's greyscale is way off, obviously the only option is a full ISF. However, with a well done set, Avia get one very very close if done correctly.
My Sony 34" XBR is done with Avia, sure the colors are slightly oversaturated (mainly red and a bit of green), but it is not worth the $300-$500 for a 5% or less increase in accuracy. Of course, I do have some limited calibration experience.
I may pick up a device (light meter/colormeter) when I have some extra cash, but for now what I have is close enough.
For a person with some of the new Samsungs, 650 series on up, movie mode is essentially an ISF set up from any of the reviews I have seen. Run the Avia disc for small fine tuning and you would be all set.