I just paid mine - thanks to the person who resurrected an old post as a reminder!
Not huge, but if you booked your cruise before the annual increase, you pay the old rate if you pre-pay, the new rate if you pay onboard. And I cruise in 2 days, so not much of a loan to NCL. It will all be on the same CC statement at this point. You can always wait until just before you sail if you want it paid before you board, you don't have to pay it at final payment.