I got into the summer program that my professors sent LORs to - should I send an e-mail telling them I was accepted? Should I thank my old professors in person? I am not sure about the etiquette of such things - and it seems rude to not acknowledge them (or tell them of my acceptance). Your thoughts?
I know times have changed, but I’ve been taught that it’s nice to send a handwritten thank you letter. It doesn’t have to be fancy. Just thanking them for their support, what you hope to do during and after the program. Then for me, those people get added to my yearly update email list where I let my most supportive professors and mentors know what I’ve been up to and my future plans. Here’s an example: http://gradschool.about.com/cs/askingforletters/q t…
I tend to agree that a handwritten letter is the standard for an LOR. However, it definitely depends on your relationship with the writer.
I took the manager that wrote the professional LOR for my post-bacc out to a nice lunch, but no letter. I communicate pretty regularly via email with the bio instructor that wrote one of my academic LORs and we see each other on campus often. I emailed him an update and a thank you as soon as I was accepted into my post-bacc. A handwritten note would have seemed a little goofy.
If I end up getting LORs (fingers crossed) from faculty during the post-bacc, I will probably go with the handwritten note.
Hand written note.
+1 for hand written note. That is a safe, inexpensive means of showing your appreciation.
Will do with the handwritten note. I am so computer oriented I had a very dim remembrance that yeah, a handwritten note is the way to go. 
Thank you, everyone, for your responses.