AppleInsider 
has a wonderful comparison of Microsoft’s upcoming PowerPoint 2008 (which will be released as part of Office 2008 for Mac in January) with Apple’s Keynote 4.0 (part of iWork ’08). The best quote of this review?
While a dedicated PowerPoint user could probably eventually deliver many of the effects possible in Keynote, doing so would be far more work and a lot less pleasant. The templates in PowerPoint are anemic and simplistic, the editing tools are spotty and limited, and the application seems intent on forcing you to make use of canned ideas rather that providing you the tools to actually create your own projects.
The main reason TechnoEsq recommends attorneys use Keynote in presentations is due to the lack of finishing touches in PowerPoint which enable quick, quality slides to be created with ease. Unfortunately, the limits of PowerPoint aren’t relegated to the Mac version of Office; they flow over into and are expounded by the limitations of Windows Vista and XP in Office 2007. This article goes into detail about the limitations of both Keynote 4.0 and PowerPoint 2008.
TechnoEsq believes the greatest Keynote feature is the ability to export presentations created for attorneys directly into QuickTime movies This allows our non-Mac customers to play our presentations on any PC, using the keyboard to advance transitions.