The comic between Estonia and Latvia. Latvia is contemplating making cookies for Christmas, but thinks no one will eat them. Suddenly Estonia shows up, and he and Latvia have an adorable conversation where Estonia asks to come over and see Latvia's Christmas tree. One they part, Latvia, with the barest hint of a smile, decides to give some of his cookies to Estonia this year.
Germany takes a cute group picture of the gang. Austria hides his face because he's embarassed.
Sweden coming in and helping Finland out with his airplanes and firearms, anyone?
The Nordic Family (Sweden, Finland, Denmark, Norway, and Iceland... and Sealand) banding together in order to get Ladnoia to believe in Santa... Finland going so far as to find a toy shop owner to dress up as Santa and fly the sleigh with him, because Ladonia wouldn't believe in him if it was just Finland flying the sleigh.
England gets mad at America for overproducing everything, then remembers how little he used to have back when he was a colony and wonders if that's why he does it. He then stops bothering him about it and gives him chocolate.
Rome and Germania are watching the festivities from heaven. Rome asks if he "knows any cute ones", and Germania looks at Germany, Prussia, Austria, Switzerland and Sweden. Rome: "I meant cute girls, not your family! You're a doting parent yourself aren't ya!"
Hima spends an entire week fighting a really bad cold. The first thing he says when he's finally strong enough to draw and get on the computer? "Sorry I took so long. And sorry for making you worry so much". Then he adds chibimerica to the deal as if to try and make up for it. Dammit Hima, we're just glad to know you're okay!!
The fandom. There are group hugs almost every other page and when somebody drops out for sleep/food/real life, they get anywhere from five to fifteen comments wishing them good-bye.
At some point, a few of them took on roles and the nicknames stuck; now there's a full-out family that everyone is included in.
An incomplete list of this family can be found here.
Also, at the beginning of Thread 12 they began discussing shipping. However, they managed to carry it on for 10+ pages and never was there a single insult, bash, or anything other than "Oh, that's cool!" "I never thought of it that way!" "This ship is win!"
The user Darkangel160 said of the fandom, "We don't have shipping wars here... we ship the wars" because of how everyone was getting along (and shipping Hussieruya, which is Andrew Hussie of Homestuck with Himaruya of Hetalia.
As soon as it hit New Years in Japan, a fandom-wide hugfest occured with plenty of hugs for Himaruya. Starts here: 
When the update got delayed, people started sharing how they got into Hetalia. Cue the most heartwarming, tearjerking stories yet.
Thread 25 looked like it was just as cursed as Thread 13, so in order to fend of HST, the fans began posting nostalgic videos from favorite childhood TV shows and pictures of Darth Vader — they were remembering Bob Anderson.
A strip (the second one down) was released that contained some England/Japan Ship Tease after the shippers for that pair had been getting sad for awhile due to the lack of it. For one reason or another, most of them weren't on the thread at that exact moment. The reaction of the non-England/Japan fans? "I can't wait until they see this, it's going to make their day."