Regarding the peer-reviewing process, in conferences in my field (civil engineering), sometimes we receive 100-200 papers. After the review process is over, typically, the top 10% get to be presented in key sessions. Then, top 30-50% of accepted papers will be presented in regular sessions. Finally, the rest will be presented as posters (due to lack of time/rooms) or declined! So, you can say that there is some sort of a peer reviewing process involved.
In my case, I have always added the posters under "Presentations and Poster contributions in Conferences" section in my resume (and I can assure you that I really do not need to do that). This section falls right after "Articles published in conference proceedings". I do not see the point of doing some work and spending time on preparing a poster or an abstract and not take credit for it. Every small contribution is valuable. I doubt that whoever is interested in your resume will consider posters as a major contribution. Most likely they will skim through it or completely skip it. Peer reviewed journal articles are the most important part of a researcher's career (in my field).