Also curious about this as well, I was second author on an abstract presented but did not present it or go to the conference.

Absolutely!! List everything you can in the research. Very few med students get the honor of being first author. Abstracts will count. Just make sure that you know about the project and you are honest about your role. You will be asked about it on the interview trail. There is nothing interviewers dislike more than someone fumbling over their listed research. Can raise red flags.

should these be listed as "publisehd" abstracts, or just a poster/oral presentation? The way eras has them categorized lists Abstracts in the same category as publications... and while the abstracts I've been on were in fact "published" at these meetings I always viewed them as more of a "presentation"...

I think of published as in a journal. It is not clear where to draw the line. If it was just published in the booklet handed out for the conference, that may or may not count depending on the caliber of the conference. Use your discretion. You have to list where it was published, so if it doesn't feel right to you to list it as published just list it as a poster. I don't think you could go wrong either way. You are making an effort to be as honest as possible. Just include as much information as you can about it. The important thing is for it to show up on your application.

Cheers. Good luck!