It's the new coolness:
The danger, of course, if that you'll use your habits developed for the old medium in this new way of doing business. The two major downfalls that I've seen (in my four hours of using it) is either doing a boring old PowerPoint presentation in Prezi, or turning on all the uber cool animations and making the Geocities of Presentations.
But this - while perhaps flirting with the Geocities pitfall - will never be confused with a boring old Powerpoint slide show:
Prezi makes you understand your story, what you want to communicate to the listeners. It seems essentially impossible to do the old PowerPoint "Show up and throw up" lazy presenter cop out: I've got 87 slides here, so stop me when you see something you like.
I expect that I'll be playing with this for a month before I make something worth having. But then I'll have something worth having. Cool stuff. The rabbit hole goes deep. And who ever though anyone would say that about a PowerPoint replacement?