Yes, halfway through our trip. But, only because the roadtrip to the resort adds 1.5 days each way to the vacation, meaning more clothes than you would need for a 7 day stay if you were flying. Plus, everyone has at least one "favorite" pair of shorts or top they want to wear more than once.
We usually go to the laundromat on site (which is never too far from the room) - after the smaller kids go to sleep. By day 4 onsite, we've got 6 days worth of clothes to wash, which is about 3 loads of laundry. Oldest DD is put in charge in case anybody wakes up. Washing takes only 45 minutes, but the drying takes FOREVER - seriously, it takes 2-3 full cycles to get things dry - ugh!. LOL. DH typically runs back up to the room once or twice to check and make sure everyone's ok. The rest of the time we sit and chat and discuss our plans for the next day. I make sure to bring park maps and a pen with me! We've actually never run into anyone else in the laundry room on any of our trips - always had it all to ourselves, so no waiting for other people to finish using the machines. Either not a lot of people do laundry on vacation, or we just had good luck.