I support ACIM, but also give some caveats:
- ACIM (the workbook) calibrates at 600 per Hawkins' Map of Consciousness Scale.
- ACIM (the text) calibrates at 550, due to the mistake of demonizing the ego as something evil to be conquered instead of accepting it compassionately and healing it
- both do not calibrate at 1000, meaning that there are errors in it and it is not infallible
During Dr. Hawkins' spiritual journey, he used to teach ACIM, and he said that he had seen people with every kind of disease known to mankind spontaneously remit due to intense spiritual work with ACIM.
I think of ACIM (the workbook) as a handy practical guide to enlightenment, and NOT a source of serious spiritual study. To really understand spirituality I look to mystics like Dr. Hawkins, Ramana Maharshi and Nisargadatta Maharaj, and traditions like Advaita Vedanta, Buddhism, etc. They put everything in the right perspective and context. But in the end, spirituality is not just something to understand on the level of mind, but something to be put into practice in daily life -- and that is where ACIM plays its part. Don't look into it for understanding, but look into it for the practical exercises. You can just do the exercises without reading the explanations or the text, and you'll probably get close to all of the benefits in it. The understandings will come later, by experiential revelation, which is what really matters.
The key lesson in ACIM is forgiveness, and just learning that one lesson thoroughly will take you all the way up the levels of consciousness.
And to address the issues other people have raised... I see two answers to them:
1) those people did not get the point of the exercises, and did not really improve (which is ok, because spiritual work takes time -- at least they're not whining about their circumstances like before, lol!
)
2) these changes are changes in perception / context, not in content. People may still have shitty lives, but to them it really doesn't matter anymore. This is where spiritual work really pays off.
I personally have done some of the lessons in ACIM, and I think they're great. The "floaty" or "dreamy" effect you get is probably due to semi-expanded state of consciousness beyond what you're normally used to. After studying nonduality for a year or so, all the ACIM stuff makes perfect sense 
My $.02 
Namaste