Re: The REAL real pain
The real pain is that if you're registered for sales tax you have to make a monthly return even if you don't owe any, and if you don't send in a return there's a penalty.
I ran into that when I got a temporary seller's permit in Illinois. They didn't seem to understand what "temporary" meant. Eventually I solved it by sending them a thick stack of $0 returns and asking them to cancel the business license.
Furthermore, when I was registered for sales tax they made me post a bond. It wasn't much, it was $500, but it would be a serious problem to have to post one for all 50 states.
As I recall the new rules only apply to companies with over $100,000 in annual sales. It's not like every mom-and-pop will have to post bond. Also, I think only 15 or so states actually require one. (Not every state charges sales tax, and not every state that does requires a bond, and ones that do require bonds often only require them for a specific set of products, like tobacco.) So it's probably not as dire as all that.