[Updated after comments here and elsewhere]
Yes, I'm still fascinated by this. And thanks to commenters here and on twitter, I have some preliminary results. Obviously not something that would hold up to rigorous scrutiny, but enough that I figured I should make a record of it before moving on.
It appears that there is a polling place bake sale zone and a zone in which there are no bake sales, with the former including the northeast, the middle west, and spreading south as some of the border states. And then there's a zone without bake sales on election day which is made up of the deep south including Texas, the southwest and mountain west, and the west coast.
Okay, specifics. We have reports of bake sales in the following states: MA, CT, ME, NH, VT, NYC, NJ, PA, OH, MI, MN, WI, MD, VA, TN. [UPDATE: add an upstate NY, a Chicago, a New Orleans, and one in Houston!]
And we have specific reports of the absence of bake sales in TX, MS, CA, CO, MT and IL. [UPDATE: and Nebraska] Also IN, but it wasn't a school. I'm strongly inclined to assume that both Indiana and Illinois have them, but don't have a report yet; I'm also strongly inclined to believe that Arizona doesn't, since I have no memory of knowing about it. Multiple reports from New York City, but only one negative report from upstate...I'll be surprised if they are limited to the city, but I can't confirm anything more.
Not included here are absences in states which do have them, since no one thinks that all polling places anywhere have bake sales. I'm also not counting refreshments served at polling places to those hanging out there all day. Just bake sales.
Although it turns out that not all bake sales were in schools. It seems to be the most popular location, but then again there are lots of polling places in schools, so it's hard to know what to make of that.
If anyone else has reports to add, I'll probably just update this post, so keep them coming!