I also use LaTeX for presentations, and my approach to the sharing slides problem is to first convert other people's slides to PDF (if they aren't already in PDF), then create a Makefile that uses GhostScript to splice and reweave the output of SLiTeX with the slides I want to import.
If someone wants to use my slides in PowerPoint ... well, they have the PDF, and PowerPoint can import PDFs as images at least, right?