Can I add a poster session to my CV if I wasn't there but had my name on it? I worked on research that was presented as a poster session at a conference. However, I was not the first author and didn't attend the conference, but my name was on the poster. Is it still okay to list the session on my CV?

(I'm aware that poster sessions are not a big deal, but I'm very early in my research career, and I did real work on this project, so I'd like to be able to take some credit for collaborating as long as it's ethical to do so.)

Update: Since the field seems to be an important factor, this would be in linguistics.
This might depend on the field. In computer science, for example, conferences are more than just "get togethers" and serious research is often first presented there and might be published only in proceedings. In such a case it would be good for a young researcher, especially a student, to list poster presentations on a CV. 

As you say, it isn't just the "presentation" that is important. It is the work that went into the research behind it. If there is no other publication of that research at present, list it, but be clear. 

I've learned some interesting things walking through poster sessions and talking to students about their research. It was the research that was important, not whose face I was looking at.