The sorting hat, for the most part, took a lot of pride in his sorting capabilities (he was created for that sole purpose, after all). The first fifty years were some of the hardest, the founders were still working out the kinks and determining exactly what kind of people they wanted in their respective houses. This, obviously, led to some misplacement of the houses, but he insists that he wasn't off by too much. As the centuries passed, the sorting hat found the job getting much easier. Instead of being afraid of misplacing the young first years as they'd walk up to him, he would take amusement in their facial expressions (many had older siblings that had told them he was a force to be reckoned with...and would possibly eat their heads off). So, with time, he came to enjoy the welcome ceremony and he even came up with new songs to welcome the students with (in the very long time between ceremonies). In fact, he became so confident that he once claimed he hadn't misplaced any student after his first century.
Of course, this just had to come tumbling down in 1999. They had opened the school on September 1st, same as every year before that (even though they still hadn't finished reconstructing the Astronomy Tower). The entering class was much smaller and many of the previous year's students didn't return, causing a drop of at least two-thirds of the student body. Although most all of the Gryffindors and Hufflepuffs stayed, three-fourths of the Slytherin house left, and only one-third of the Ravenclaws stayed. The incoming first years didn't know much about what had just happened, but they knew enough to be at least mildly frightened. The returning students were on defense coming in, most having been at school and fought during the Battle of Hogwarts.
Nevertheless, the sorting hat sang the song he'd prepared the school-year before and welcomed the first-years as he would any other year. For the most part, the sorting had gone as expected. A boy by the name of Dominic Cobb (a dirty blonde, blue-eyed, mischief maker that was one of the few smart enough to pull off the pranks he'd planned) was an obvious shoo-in for Gryffindor. Then there was Charles Eames (a mischief-maker that blatantly disregarded rules and had an act-before-you-think mentality). The boy angrily snapped at the sorting hat for "taking so bloody long to pick" and was promptly placed in Slytherin without a second thought. However, the challenge that year came in the form of Arthur Clarke. A young black-haired and brown-eyed boy that was as clever as a Ravenclaw, loyal and patient as a Hufflepuff, brave as a Gryffindor, yet could be as cunning as a Slytherin when crossed. The sorting hat spent two full minutes picking around Arthur's brain, looking at his little traits, eccentricities, that would help him be sorted into the right house.
In the end, Arthur became a Ravenclaw that dressed like a Slytherin (Cobb always would tease him for wearing such nice suits under his robes), had the loyalty and patience of a Hufflepuff (except when Eames would act like a right prick), and would face any bully without a second thought (he once took on a third year, promptly hexing the teenager so that he'd throw-up continuously until the end of the day).
The sorting hat couldn't help but hear bits of gossip from the portraits and ghosts as they passed through the headmistress's office and he kept tabs on Arthur, the only boy he had trouble sorting in the last century. The sorting hat wasn't surprised when he learned that Dominic Cobb had befriended him (he heard that they shared a compartment on the way over to Hogwarts). However, he was surprised when Dominic introduced Eames to Arthur and they became friends (albeit slowly at first). The sorting hat kept entertained by hearing tales of Eames and Cobb's pranks and he smirked whenever he'd hear about Eames, Cobb, and Arthur plotting revenge on somebody that had crossed one of them. As the years passed he heard more about the trio, sometimes four-some when Saito joined in, and smiled as heard of Cobb's many attempts to woo Mal (reminding the sorting hat of Lily and James Potter when they had attended Hogwarts).
The sorting hat was pleased when he heard about Arthur's crush on a Ravenclaw girl a year below him. Her name was Ariadne and she was a relatively easy one to sort, despite the odd circumstances. She was a transfer student from Beauxbatons and came in her third year. Her parents had passed away during the war while they were on a business trip to London, leaving her to move in with her aunt and uncle. Her aunt and uncle insisted she stay closer to home and immediately enrolled her in Hogwarts. As unconventional as it was, Hogwarts was still in need of students and McGonagall arranged for her to come in and be privately sorted.
Nervous and shy, Ariadne was sorted in the headmistress's office. She was obviously quiet, but once the sorting hat was placed on her head he realized just how clever and artistic she was behind that mask of timidity. She was declared a Ravenclaw just three seconds after the sorting hat was placed on her head.
Two years after Ariadne had graduated (top of her class due to her cleverness which reminded the Hat distinctly of a certain Granger-turned-Weasley), the sorting hat caught a glimpse of the paper Headmistress McGonagall was reading. The headmistress was going through the announcements section of the Daily Prophet and the sorting hat saw a small picture of Ariadne and Arthur, both laughing and seemingly talking animatedly. Under it detailed their impromptu marriage (not quite as fast as when Mal and Dom eloped the day of graduation, but small and quiet nonetheless). It was at their flat in muggle London and with only their closest friends and family. However, it suited the two. They were much too down-to-earth for some sort of extravagant wedding like the ones that the Malfoys or the Zabinis usually had, despite the fact that Arthur came from a particularly well-to-do pureblood family. (Although, it might be a new trend since the sorting hat once heard that Draco Malfoy and Astoria Greengrass had eloped, to the absolute horror of their parents). Arthur and Ariadne had a low-key relationship, a relationship that only a shy architect and a serious auror-in-training could have.