Halloween 1992- WDW (Magic Kingdom)
My brothers and I wore costumes on the plane, but I was afraid my Belle dress would be ruined in the park...I was 7; that would have been traumatic, so I changed.. This was in a relatively quiet season (I LOVED September through November when I was on the College Program...), and before they even had anything like Mickey's Not So Scary Halloween Party, so it wasn't terribly busy. I remember waiting in a decent line at Haunted Mansion, but not having to work too hard to get spots for Fantasy in the Sky that night.
Holidays at WDW 2005- College Program
Memorial Day- Epcot
Not really much different than any other day in the summer in terms of crowds...it was very busy, but not particularly awful. And the heat wasn't quite as hot and humid as it gets as the summer progresses.
Fathers' Day- Epcot
Again...a Sunday in June, so busy, but not much more or less than any other summer day.
Fourth of July- Epcot and MGM
OK, this was when it got brutal...the heat and humidity were in full swing, and the park was really busy, even for really busy season. Luckily, the Guests at Epcot seemed pretty happy and prepared for what greeted them.
One of my friends and I went to MGM after work that night to see the fireworks there (we didn't want to try to get to MK, and we'd heard Epcot's were amazing, but for once I needed out of my park). MGM's were cool...THAT was a MOB SCENE though. I can't even imagine what the crowds at MK and Epcot must have been at night. BUT! On the flipside...after the fireworks, seemingly everyone left, so we were able to stop for a quick service dinner (with no problem finding a seat), and take two back-to-back rides on Rock'n'Roller Coaster with no wait right before the park closed, which was only about an hour after they'd done the fireworks.
Labor Day- Epcot
DEAD. Apparently that's not typical; we think a lot of the abnormally small crowds could be attributed to Hurricane Katrina. My dad's been there for Labor Day and said it was useless trying to do much, but this year it was very, very slow.
Halloween- Epcot
Fairly normal...moderate crowd levels; my shift started late afternoon, and it was pretty slow until around 7 when it got fairly busy, but still nothing like a summer night in terms of crowds, or temperature...a nice cool spell came then!
Side note on Halloween:
I went to Mickey's Not So Scary Halloween Party twice, and it was amazing...yes, the ticketed events are pretty crowded, but a lot of people spent the evening trick or treating and/or just taking in atmosphere. You had to get a parade and firework spot fairly early, and some food lines were long, but if you wanted to do rides, they seemed to be all walk-ons. Although, we really only felt we had to do Haunted Mansion, ride-wise, but even for a Halloween event, it didn't have a long line at either party.
Thanksgiving- Epcot
Significantly busier than early in November, but still not on the same level as most summer days. Crowds are also easier to take when you're not dying of heat.
Christmas Eve- Downtown Disney
By some twist of fate, I got Christmas Eve off, but I did some last-minute shopping at Downtown Disney. It was busy, but not nearly the mob scene I expected.
Christmas Day- Epcot
I was lucky and had a morning shift...it was rather slow in the morning, but it was DEFINITELY getting to be really crowded by the time I left. I didn't see the highest crowd point since I was off by mid-afternoon, but it was starting to fill up a lot faster than it had earlier in the day.
Side note on Christmas: Went to Mickey's Very Merry Christmas Party in mid-December, and that was really nice...like the Halloween party, you want to be early for the parade and fireworks, but again, the lines weren't long (I think we did Space Mountain twice and Buzz Lightyear's Space Ranger Spin once, since we'd missed Tomorrowland when we'd been at MK earlier in the day...we being my parents and me; I took some time off when they visited. They came from the 10th through 14th of December, and that was a great time; the crowds were moderate to light except in MGM when they lit the Osborne Spectacle of Lights on the night of the 10th...but that was either a Friday or Saturday night.)
New Year's Eve 2005- Epcot
ABSOLUTELY INSANE. I started work around 2 in the afternoon and could barely move to walk to my location. New Year's is listed as one of the busiest times of the year in all the WDW Guidebooks; that's an understatement. It was easily the busiest day that I worked. The people who were there to enjoy the atmosphere and be in WDW when the New Year came in had fun, but there were a lot of people in bad moods because they hadn't expected crowded to mean as crowded as it did. I thought it was a pretty fun day, though; yes, it was annoying that someone decided that every WDW guest would get a free noisemaker on New Years Eve and we had to listen to honking plastic horns all night, but the whole thing was really too funny to be upset over, IMO. And I got off of work just in time to get to see the New Year's Fireworks which were INCREDIBLE. If you can handle insane crowds, the fireworks ARE worth seeing. But if you've never been to WDW before...don't pick New Year's Eve to go.
New Year's Day, on the other hand, was a slow day. Go figure.
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Valentine's Day 2006- Disneyland
The weekend before V-Day was busy, but...it was a weekend at Disneyland, and during the Happiest Homecoming on Earth. My mom and I managed to do a lot on the weekend without going too crazy, and we saved all of what we didn't get to on Saturday and Sunday the 11th and 12th for Valentine's Day (we went to the Studio in Burbank on the 13th). It was very very pleasant; we didn't have long lines for anything; the difference between an off-season WEEKEND (oxymoron?

) and off-season WEEKDAY was amazing, even though it was a holiday. We saw everything that we wanted to in both Disneyland and DCA (and meet lots of characters!) without wearing ourselves out too hard. (We did observe a LOT of PDA around the parks that whole trip though, but nothing that was inappropriate.)