Somebody set me straight on this subject here a while back. Sub 10,000 pounders do not have to log unless hauling commercial freight in NY or KY, but NY and KY don't really enforce that law.
Here's the deal on weigh stations- it's just a matter of reading the sign, and it can't hurt to go through. Some states state a weight "Over 5 tons, etc." some say all commercial vehicles, some say "all trucks". In my book a van isn't a truck so I wouldn't bother. In interstate cargo van is a commercial vehicle so I would go through. I wish there would be a nationwide standard for this stuff rather than individual states making up their own confusing rules. The safety director where I run told me that the vans and cube trucks with the company are just about never bothered with by the DOT.