Quoted from YeOldPinPlayer:
Texas has a similar law.
1. What "purchases" are subject to use tax?
...You used property purchased from an out-of-state retailer. In general, if you purchase a taxable item from an out-of-state retailer without paying Texas tax and use the property in Texas the purchase is subject to use tax and must be reported.
Seems like CA Pinsiders are the ones who've been contacted to pay up....has this happened anywhere else?