We have never done laundry on the ship - even when we were right across the hall from the laundry room on an 11 nighter. We are lucky that DH has Platinum status on Delta so we don't pay for up to 2 bags. We just bring what we need and plan on wearing things more than once. I've been known to wash out a couple of things in the sink if need be, but other than that if we needed anything else washed or pressed we would just send it out to be done.
I was intrigued by Dug720's repose. I completely get what she is saying but I'll add a slightly different twist on it. As I
do have laundry facilities at my home, the idea of having to take my laundry somewhere, worry about finding a washer, either sitting and baby sitting it or timing it to get back at just the right time is foreign to me - Nope! Not interested in doing that on vacation. Now when we are at the beach it's a entirely different story. We rent a house every year for just a week and I ALWAYS do laundry. We just bring a few things with the idea I'll wash at least once or twice. The house has a laundry room, so I just throw in a load, head to the beach and forget about it until we get back - kind of like at home. That doesn't impact my vacation at all, but worrying about doing laundry on a cruise ship - not for me, but to each his own!

Obviously a LOT of people do not agree with me, though, as the laundry room across the hall on our last cruise was always packed!