my pathfinder can also see word files. I want to preview both excel and powerpoint files as well, especially the latter. I think steve did show support for excel preview in cover flow but not for ppt files (although keynote, yes. but keynote is not that powerful yet IMO and cross-compatible with windows)
I use Keynote exclusively. It is way, way, way, way better than Powerpoint. Really. Try it out for yourself if you don't believe me. It is more powerful in any way you can imagine - and on the top of that, it just makes better presentations.
I go to plenty of scientific meetings, and I can tell by naked eye if the presentation has been done in PowerPoint. Microsoft's typesetting engine is THAT bad, really. And don't start me on the included templates, or the alignment tools (or lack thereof) in Powerpoint. Or the way Powerpoint renders shadows (never, ever do that to yourself). Bleh. And bleh again.
Keynote is also lives perfectly well with Windows. You can export your presentations as PDF files, as Quicktime movies, or as sets of images. Your transitions will be preserved if you choose Quicktime export. You can even export your presentations in Powerpoint format, should you ever want to.