If it’s more or less an Ohio holiday … why are there Sweetest Day greeting cards down here in Louisiana? Never seen one of these cards bought or given. There’s no way those things are moving fast enough to justify creating a holiday from whole cloth. 
I upfront told my (now) wife when we started dating that she could expect to never receive anything on sweetest day. She took it well. Now I’ll sometime wish a happy sweetest day to her in a drippy sarcastic tone.
She makes out pretty well on Valentine’s and over the year, though.
I’m from the suburbs of Cleveland, so I guess that’s prime territory for this holiday, but I’ve only heard of it a handful of times. I don’t think anyone takes it seriously - except drama queen girlfriends who have an excuse to make demands.
I’ve never heard of it before this thread but I went to Target today and their card aisle had a section for Sweetest Day. WTF? I live in Florida!
To avoid Sweetest Day trauma, I take the precaution of avoiding having a sweetheart.
I’d heard of this - not exactly sure under what circumstances as I’ve lived in NE FL or the mid Atlantic area since 1980. But in our household, it’s treated the same as Valentine’s day. That is, we ignore it.
It works for us. 
I grew up in the Detroit burbs, so I always remember having it around as a second V-day. In high school it was a big fundraiser opportunity for schools, let the honor society or spanish club or whatever sell carnations to be delivered in class for Sweetest Day. Of course then you and your friends all had to buy them for each other so you wouldn’t appear unloved. (ugh)
<hijack>Hey, Tina Fey had a similar scene in Mean Girls, and she grew up in Pennsylvania, which is just barely a Great Lakes state, hmm. <end hijack>
I didn’t buy any giftage for my boyfriend but I am making him a nice dinner, and I’m actually taking the time to dress up and bother with jewelry and makeup and such for him, so there’s the extent of the effort. I cook for him regularly and could be pretty any time, but rarely do so it counts as effort, right?