I have reflected often on this quote attributed to Charles Haddon Spurgeon:
"It's better to preach to a laughing man than a sleeping one."
Motivational speaker and author, Zig Zigler, once said that he built something humorous every two to three minutes into his presentations. He realized 1) that the attention span of his listeners was not very long and 2) humor has a way of reconnecting with those whose minds have wandered off.
To be sure, a sermon is not designed to be a comedy monologue. In its simpliest form, the sermon is the opportunity to proclaim the good news of the Gospel of Jesus Christ. But the utilization of humor or visual aids or power point slides (so long as they are not overdone) help the speaker engage his hearers, enabling the message to be better heard.
I agree with Spurgeon - I'd rather preach to a person who is fully engaged than one that I've sent to la-la land!