Our family was on the Magic last week. On Thursday, you get a sheet of paper with the recommended tipping amounts and envelopes for each person. If you fill it out and take it guest services, they will charge your account the amounts you have filled in and give you vouchers for the envelope. We did the recommeded amounts which added up to just over $300 for a family of 4 on a 7 day cruise. We also put some extra cash in the envelope for our dinning room staff since they when beyond the call of duty due to some food allergies. I am sure if you do the vouchers, it gets added to their paycheck and probably taxed - but with some of it in cash, well I won't tell anyone. I am not sure if the staff pool their tips or not.
PS - I don't mind tipping if the service warrants it, but automatically adding a 15% tip to a bar bill (and then having a line for an additional tip) is like finger nails on a chalkboard for me.
PS2 - avoid the sail-away drinks they serve while on deck - $7.95+tip, but you get to keep the plastic glass. Kind of sneaky if you ask me..