I'm afraid I kind of have to disagree. Ambien isn't like other hypnotics, and it acts marginally like benzodiazepenes, acting on the GABA-BZ receptors in the brain.
Usually, it will just knock you out. If you intentionally fight to stay conscious however, it does have the effects people are talking about. Like I said before, I would compare the effects to deleriants like diphenhydramine (benadryl) or dimenhydrinate (dramamine), which drastically alters a persons perception of reality at higher levels. I'd suggest you look here:
http://erowid.org/experiences/subs/exp_Pharms_Zolpidem.shtml , and see the evidence. I also speak from personal experience, and I can assure you, I don't see things in my everyday life.
Nobody seems to have any idea what the mechanism is that actually produces these altered states. By all reason, like you said, it shouldn't, according to the pharmacological properties of Ambien (as least what we know of them). It hasn't been looked into that deeply, primarily because pharmaceutical companies don't want anyone too, as it would compromise how easily they are able to dispense the drug. But several medical professionals have noted it in literature, and there has even been media coverage talking about it; because of the anterograde amnesia effect of Ambien, however, it's usually attributed simply to "sleep-walking", and when taking larger doses, people do tend to black much more of the experience out. But the person never actually falls asleep, and can interact completely with their environment. They've even started research utilizing this altered state, because it seems to have the peculiar effect of waking people from permanent vegetative states, to the point where the subject is able to carry on a conversation, but then returns to their vegetative state once the effects wear off.
I'd advise you to read the experience reports, look at the media coverage, etcetera. It does indeed have the effects people are talking about. As I said before, it's not even remotely understood why it does this. Then again, the visual effects of LSD-25 are not medically understood at all, either.
~Ethno