Doing a bit of research on the subject. Arizona seems to be the tightest with a posted minimum weight, any commercial vehicle over 1,000 lb has to scale (so far, messenger bikers don't need to scale anywhere--- how long does that last, I wonder). Wyoming may be the toughest, expect to have to have just short of a full cavity search there if the lies I read were any indication.
Most of the stuff I've read indicates that even in the states where a vehicle my size (G2500 Chevy CV) does have to scale it's likely to be green-lighted through unless something is obviously wrong-- like trying to make it weigh 16,000 lbs for example. Mainly, even in those states where they do weigh the light vehicles, they don't want to waste too much time with us because they're really after the heavier trucks.
Special note: Even if you don't have to scale, you still have to use good sense. I recently turned down a run because the load, at 3,600 lbs, would have pushed me overweight. Maybe not by much, but maybe by enough that an observant trooper would notice and create a problem. If the vehicle looks wrong to him, he may put you on the scale even if it is below the minimum required to scale in that state. In my case, I have Illinois "B" plates and that gives me 8,000 lbs GVW, I have to keep that in mind.