Polls are a great way to get informal feedback and start discussion around the results. Yammer's poll allows only one choice to be made.
So my here's my suggestion for creating a Yammer poll that allows more than one response.
Creating a "More than one answer" Poll
1. Start your choice with a letter, so multiple choices can be referred to in a Reply.
2. Offer a "More than one answer" choice.
3. Attachments are always a handy option.
Answering the Poll
4. Choose "More than one answer"
5. Reply with the choices you'd make and any additional comments.