Humor in the pulpit can be very dangerous. It's like a narcotic. Your people will love it (how much more entertaining to hear you riff on something than to teach Leviticus or talk about sin). You'll love it (less sleeping, more laughing at how hilarious you are!). And the temptation will be for you to give the people more of what they want and less of what they need. I listen to about 10 sermons a week, and some of the guys I listen to are both funny and really good teachers. But here's what I notice... they have to tell three jokes for every one that really lands. Two out of three just kind of linger there and die. And so the whole sermon feels like it's being interuppted by second rate comedy. Over time, my fear is that the people will come hungry for your humor and not necessarily for the word of God. They will be dependent on you and your charisma and your sense of humor, and you'll never be able to plant churches because you can't find anyone else as funny as you are, and so you'll have to pipe your sermons into other locations.
Humor In Preaching
Michael McKinley over at 9 Marks recently posted a good word on the use of humor in the pulpit.