Take a Walk on the Wide Slide
Widescreen displays are popping up everywhere. Increasingly it's the default screen format for new products such as HDTV's, laptops and even handheld game systems. Widescreen plasma screens are becoming very popular in boardrooms as a presentation display. Even the US Military uses it for their briefings.
What defines a widescreen is it's shape, usually expressed as a ratio of width to height. Standard televisions and most computer screens use a 4:3 aspect ratio. HDTV's use a 16:9 ratio. And widescreen laptops are usually 16:10. The aspect ratios we see today have generally emerged from their use in cinema. You can find more information on this here.
Widescreen Advantages
Using widescreens for presentation display is a great way to use all the available pixels on these new screens around us. It's definitely trendy. But there are advantages to presenting in widescreen format. The extra room allows side by side material to fit more easily. And the cinematic shape adds a bit of drama to your slides.

Setting it Up
In PowerPoint 2007 we make setting up widescreen presentations easier; we've added options for them in the Page Setup dialog. On the Design Tab, click the dialog launcher in the Page Setup section. Click the dropdown list called Slides Sized For -- this will give you two new options for On-screen shows, 16:9 and 16:10. Pick one and click OK. Your slide will change to the new shape.

IMPORTANT: you should make the change to widescreen format before you begin creating your slides. If you change from standard to widescreen format after you have content on your slides many objects will be stretched wider and distort their appearance.
(PowerPoint 2003 users: you can play along, too. Go to File | Page Setup... while there are no built-in options you can simply enter 16" for your slide width and 9" for your slide height.)
Widescreen, not required.
At this point, most laptops and presentation projectors are not widescreen. But you can still present in widescreen format. PowerPoint's slide show always fits your slides to the available screen space in much the same way widescreen movies can be displayed on standard televisions -- in "letterbox" format with black bars at the top and bottom.
So anyone really can start presenting 16:9 today. Get out there. Go wide.
Howard Cooperstein