Tone, schmone; there is no such thing as a formal or informal presentation! There is no such thing as a technical presentation or a PowerPoint presentation. There are only two kinds of presentations in the entire world: interesting or boring. So which one is yours going to be?
The easiest way to create a boring presentation is to try to be "formal." This typically means you have removed any and all humor, feeling, examples, stories, and interesting vignettes from your presentation. Why on earth would you want to do that?
You do want your presentation to be "informal" in the sense that you are as interesting and fun and as unpompous as you are when speaking to a friend at a comfortable restaurant. While the topic you're covering may be serious—say, financing of your company's new factory—the way you talk can be as informal and friendly as if you were talking about baseball or "Dancing with the Stars" with a friend over dinner.
Formal often means reading a speech. When is the last time you enjoyed listening to someone reading a presentation in front of you? Chances are you had to be carried out of the room on a stretcher because people thought you had died of boredom after about five minutes.
Do not forget to use contractions when you are giving a presentation—or rather, don't forget to use contractions when giving a presentation. Using contractions will make you seem informal and likeable. Not ...