I did, and I posted a picture of the letter. It was nice to let the dozens, maybe hundreds, of people that help me get to where I am know that I had finally made it. To everyone saying it's impersonal, that might be true, but it's far more practical than calling or messaging the 100+ people that I would want to tell just to say "Hey, I got into med school! Thanks and CONGRATULATE ME!!!".
IMO, I think it's fine if someone wants to post something saying that they got in, or even where they got in/where they are going to end up. It's a major life event that they worked years for, why shouldn't they share it with others? On the other hand, it would be dumb/annoying if someone was accepted to 5 or 6 schools and they posted every time they got an acceptance. It's like baby pictures. I love to hear when a friend has a kid, and maybe see pics 2-3 times per year, but when they post pictures every week (or worse, every day), that's when I'm happy fb added the 'unsubscribe' button for newsfeeds.