Sven and Jen,
Until a couple of weeks ago, I was regularly experimenting with the Gateway Hemi-Sync CDs. My chief misgiving is how boring these CDs become, given their length. So far I've concluded that they aren't worth the investment. But on one occasion (and only one) I experienced the state known as Focus 10 (mind awake/ body asleep). I was actually supposed to be experiencing Focus 12, but doubt that this distinction is meaningful. Anyway, the mind awake/body asleep state was fascinating and definitely worth exploring.
I have experienced no unpleasant "trips," but anticipate 2 possible dangers.
(1) The CDs ask the listener to request the help of unidentified benign beings whose development is equal or superior to one's own. In genuine possession cases, evil spirits sometimes mask their identity as benign figures.
(2) Once you abuptly achieve an OBE, you are subject to possible attack from negative entities. To read about this, consult the astralpulse.com website, especially the secition on "Psychic Self-Defense." There you will learn about a whole book devoted to this subject by astral adept Robert Bruce.
I have read extensively in this field and consider it helpful to use this analogy. Is it safe to use Hemi-Sync to achieve OBEs? Well, is it safe to swim at Florida's beaches? I would say yes, but point out that occasionally there are shark attacks. One OBE adept told me that she was often assaulted by low level entities while trying to return to her body. All i can say is that none of this would stop me from either astral exploration or swimming at Florida beaches. However, being blond and fair-skinned, I burn easily.

Don