The chemicals in it is not what causes the "high", its the propellants in the can.
The thing with computer duster is...its all propellent. This is what tetrafluoroethane is for, it is volatile.
In whipped cream spray bottles for example, the propellent is nitrous oxide because it doesn't effect the taste. It is also a dissociative.
(There is neither whipped cream nor nitrous oxide in computer duster.)

i mean, all the inhalants do is make you laugh and shit
That was kind of what I though too, before I read the experience reports. Enough users appearently observe extreme visual distortions and hallucinations coupled with an altered consciousness and what seems to be some kind of 'insight'. After having read the first report I even thought it may have been some fabrication, but all the others followed.

On the other subject of DXM, in and of itself the chemical seems safe physically. Some suggest the binders, fillers, waxes and glucose in the actual cough medicine are enough to stay away. There is no doubt in my mind that DXM is dangerous itself, and I have seen many people get addicted and nearly ruin their lives...for cough medicine.
It is tempting as a cheap over the counter drug psychoactive at high doses, many people begin to use and find they enjoy it, and so repeat the experience several times a week. Olneys Lesions and NMDA antagonist toxicity aside this drug can and will fuck your brain up. Frequent use can lead to delusions and what some call a dxm psychosis, this may not be permanent but effects can linger for weeks to months after your last use.
Take Juggalo420 as an example, at one point in his life he had a decent job, grades and a full four year scholarship to a near-by college. He quit his job but barely spent a day in college, dropped out and lives with his grandmother. After a breif crack cocaine binge in the summer he cleared his bank account out. Over the winter he used high doses of DXM nearly daily (while posting on this board) and went into what I would most certainly have called a DXM psychosis (search for his posts).
A bit prior to this, several of my other friends had run into DXM problems doing it for weeks at a time.
Personally, it seems to me the only way to get decently altered consciousness from DXM is to chug a bottle of the syrup which I have done a couple times and do not believe I could pull off again. (Just thinking about the taste when it comes back up...) I have vomitted every time I have done DXM, after the first and no matter the dose or form simply feel drunkish-stoned, disoriented, and what I would describe as 'dead'.

No matter, as Bill Hicks says "there are better drugs, and there are better drugs for you".