How many of you have heard speakers address the audience as a group?
Is it okay to do that?
What do you guys think?

There are a few problems here:

If I ask “How many of you,” I'm asking a group of people to answer a question that requires every individual to contribute to the answer.

Even if there were a group spokesperson who could answer, they'd feel awkward because I asked the group, not them.

And I didn't offer a way to answer if there was a way to.

A speech is a conversation between the and the individual members of the audience.

Raise your hand if you've heard a address the audience as a group.

That asks the same question but it addresses each individual, and it also provides a clear way to answer.

And the actual, numeric tallying up of the results may not be of any value. Some people don't want to share their opinions openly.

Raise your hand if you don't like your boss!

Awkward!

You can ask a question without requiring people to disclose the answer.

Do you like your boss?

That's a lot safer.

And “you guys” is just a mess!

You probably have “guys” and “gals” in your audience, along with whatever other gender mashups and monikers are popular these days. And unless you're running a summer camp for kids, they probably prefer other labels.

“You all” and “you guys” are addresses best avoided. Build rapport with each individual in the room by addressing them as such.