Concur/SAP now has an E&Y service that tracks how many days you worked in a state through your expense reports. (So obviously doesn't catch personal travel where you were working.) I was actually expecting to get hit for a couple short trips last year. I wasn't so there must have been some sort of threshold even though NC supposedly kicked in with even a single day.

But, yes, in general people pay even less attention to this than they do to paying use taxes and my accountant has never asked me anything about this kind of thing in the big questionnaire he sends me every year.