No, let me correct that, I loath Powerpoint. Clunky, cumbersome, god awful, typographic inept child of a programme. There I now feel so much better. Actually type 'I hate powerpoint' into Google and see what happens!
Being a Mac fan boy does mean I can wallow in smugness and use Keynote MOST of the time. But when sharing a document amongst many or editing a third party set of slides I am forced into the nightmare that is Powerpoint.
Yup there are a bunch of online solutions, but none that have the slick interface tools of Keynote (or its creative abilities)
http://280slides.com is a neat hybrid of PPT and Keynote from a bunch of ex-Apple bods, works on & off-line so you can share a doc amongst chums during its creation and then export to PPT or pdf or Slideshare. Lacks the full creative capability of Keynote but as a user experiance it's still way better than Powerpoint.
opps should have credited Scobleizer on highlighting @prezi via his interview with Prezi CEO @peterarvai http://bit.ly/agKNM9