From the great Presentation Zen:
[A]s you examine your work from previous talks remember this rule of thumb: if your presentation visuals taken in the aggregate (e.g., your “PowerPoint deck”) can be perfectly and completely understood without your narration, then it begs the question: why are you there?
I’m more and more convinced that presentations should not have slides with more than maybe a dozen words on them, and preferably less — obviously they won’t be very useful for someone taking a look at them afterwards, but that’s not what they’re for.
I tend to stick to that rule except for ‘code’ slides if I’m giving a technical talk. And I try and get the code sample down to the smallest chunks I can. To be honest, I’d rather present with a deck of 3x5s for notes and not bother with the projector, but I accept that some things need the reinforcement.