yes, you will have to pay sales tax at the DMV
the only real advantage would be like buying a car in Florida and driving it up (just be sure to get it rust proofed) since Florida dosn't have the harsh New England winters.
2 things to remember:
1) Cadillac looses their reslae value like crazy
2) in Florida, Cadillac's are a dime a dozen
that is how we got my car so cheap andin great condition, my mother got her car and her boyfriend got his car.