I'm seeing a lot about Yat Shevat these days; there's a sidebar proclaiming that there's no Tachanun tomorrow, with a link to a very brief exchange on the chat:
Isaac Moses: Yodeyans, Yod Chet Shevat is hereby designated a minor holiday, for farbrengens and not saying Tachanun.
DoubleAA: @IsaacMoses It was on Yat Shvat in Israel, and that is more catchy.
Isaac Moses: @DoubleAA In ChU"L, we can do both 18 and 19 ... or we could do it like Purim and Shushan Purim, and people who want double the revelry can cross the border in the evening.
DoubleAA: @IsaacMoses It has now been designated a Mi Yodeya community event. I'm expecting a detailed Halachic analysis of the rules and regulations of this holiday to be posted on Mi Yodeya sometime in the first two weeks of Adar II.
I'm clearly missing something, as the only thing I see happening on the day of its founding was a question about the targum-translation tag, another question about the art and pictures tags, and a question entitled How and why is sin passed to one's children?
Now, if it were the 17th of Shevat, I'd say it refers to this post, which ultimately evolved into our FAQ for new users. As it stands, though, what is the "holiday" celebrating?