I never used the laundry facilities either on a short cruise. I can do laundry at home and I had to do laundry on vacation when our children were younger and traveling with us. Not fun to spend your vacation in a laundromat.
I first used the laundry room when we went to Europe this year on a 12 day cruise and we were away for 19 days. I just packed some small ziploc bags of detergent and carried some fabric softener sheets and a mesh laundry bag. You can buy small boxes of detergent on the ship, but I am alergic to Tide and was afraid they might not offer other brands. I did laundry about 3 times on days at sea. The machines have a countdown timer, so you can leave your laundry and make a note of when to return, so you don't hold up the machines.
With Platinum status on our last cruise I took advantage of the free laundry service. It was nice, but took two days to get back.
Been there - done that:
2005 Holiday, Sensation, Conquest,
2006 Conquest, Celebration, Holiday,
2007 Freedom Grand Med, Holiday
2008 Fantasy & Sensation,
2009 Fantasy, Holiday & Dream Grand Med
2010 Fantasy and B2B Elation
2011 Monarch of the Seas
2012 Booked - Breeze from Barcelona 12 days