In Outlook, you could attach voting buttons to a message to get a yes/no response from the recipients. I have a user asking me how to do this in Gmail after we have migrated from exchange to Google Apps. Is this possible?
It's not strictly part of GMail, but it's very straightforward to create a Form in Google Documents.
I would love to see the Yes/No/Maybe gadget from Wave incorporated into Gmail.
Another way to conduct a poll, but which might be too technical for some, is to create mailto: hyperlinks in your message and use the "+ address feature" and your filters to capture the data.
In other words, ask your question in the subject ("Are you going to the prom?") then in the body of your message offer hyperlinks for the answer ("Yes" "No" "Maybe"). Each of those links would be a mailto: link ("mailto:youraddress+Yes@gmail.com" "mailto:youraddress+No@gmail.com" "mailto:youraddress+Maybe@gmail.com") and create filters to label the messages as they hit your inbox.
More details at this blog: http://www.labnol.org/internet/email/conduct-email-opinion-polls-with-gmail/4045/