Google+ is still a work in progress, and right now (July 2011) it doesn't have a way to make a proper poll. You could link to a Google Docs survey, but that seems like a lot of effort for a simple survey. That doesn't mean you can't have poll-like functionality. I've seen several people using this trick, but I owe a nod to Ahmed Zeeshan for being the first I saw formally suggest the idea.
Say you want to find out where your friends want to eat dinner. You can easily poll them.
- State your question in a post to your friends circle along with the instructions.
- Offer each option as a separate comment to your first post.
- Everyone in your circle can then plus one their selection.
- Count the plus ones to tally up the winning option.
- Close the post for comments if you don't want anyone else adding an option or discussing the choices.
This isn't a true polling tool. It's not anonymous, and there's no way to prevent someone from voting for more than one option. However, it's an easy enough trick that it might stick around even after (or if) Google+ offers a more formal poll tool. Using this method while leaving the comments open is very close to Google Moderator functionality, except that there's still no way to vote down an idea. You can only plus it. You can't minus it.