Usually, it's a boilerplate note, but if you write something good but unpublishable for whatever reason, they might deviate from the template. I've amassed a bunch of very nice rejections over the years!
My experience is that editors will only make the effort to write a personal rejection note if they see some potential in a writer that's worth cultivating through constructive criticism. I learned a lot about writing from the rejection letters I got over the years before I finally sold. Stanley Schmidt's rejections alone were particularly instructive.
That's still good news.
Can I make simultaneous submissions to Analog and Asimov and pick and choose if, by God's grace, I get accepted in both places?