I think one of the best things Apple could do to make iWork.com really valuable is allow to run keynote presentations from it. If you really value Keynote over PowerPoint but don't want to take a laptop everywhere it would be perfect, especially if PC's are already setup with the projector.
Upload your presentation to iwork.com, login on any computer and start playing it with animations and everything. I would pay money for that!
Also, editing documents would be nice also...
that is an excellent idea!