Reports arising from math workshops I've attended a few workshops consisting of some talks, and then maybe 10-15 hours of "group work" over the course of a week.  At one, my group more or less solved the question we set out to answer, which was mildly interesting but not particularly ambitious.  (Essentially, it was a computation a few of us had wondered about over coffee at previous conferences.)  

The organizers are hoping the groups will write up and post (arxiv+journal?) reports on the outcomes of the work.  My impression is that most people in the group were on board.  It's possible to imagine a continuing project in this direction, but I think everyone has better things to do.

In any case, we do have something to write up, and the result is even mildly amusing.  But if I'd worked it all out myself, I certainly wouldn't arXiv it or submit anywhere.  I'm faced with the possibility of being on a slightly embarrassing, very-many-author paper.

1) is there any polite way to opt to keep my name off of it? (the others are mostly more senior, but I can't really claim I didn't contribute)

2) if this thing does see the light of day, would it be acceptable to omit it from my CV, or list it in some different section?

My perspective is that of a postdoc who will be on the market a couple years from now.  How are these sorts of papers viewed by hiring committees? (My impression is that they are not uncommon these days.)
From my point of view (as someone whose eyes are still tired after reading 180 application packets...), having this on your CV would not be a negative thing.  It should of course be on a separate list from your peer reviewed journal publications along with other technical reports, conference proceedings papers, etc.  

The positive aspect of this is that it shows that you worked collaboratively with other people at the workshop.  This is a particularly valuable thing for an applied mathematics faculty member, since our department (and our dean and VP for research) want to see faculty in applied mathematics who collaborate with other mathematicians and more importantly collaborate with scientists and engineers on inter- (or trans-) disciplinary research.  

In short, don't try to avoid being listed as a coauthor, do list this on your CV in a section separate from your peer reviewed journal articles and don't worry about it hurting your chances of getting a job.