This is actually my first time that I'm prepaying gratuities, but as stated, many staff members of the cruise line have more than one job. An example, on my very first cruise on the Majesty, my dining room waiter one night after dinner was up on the pool deck after dinner for the midnight buffet and party as we were leaving Nassau. My tablemates stated that they thought that if the a member isn't senior staff, they have more than one job.
I figure on my cruise coming up, if I feel one of my staff that I tip has done something to earn extra, I can throw a few extra dollars in the envelope in addition to the prepaid vouchers I'll get.
2007 - Majesty of the Seas
2009 - Enchantment of the Seas
2010 - Freedom of the Seas