Prezi has been around for a few years now so it's a fairly mature product.
Upside: it's definitely different and can create some attractive presentations.
Downside: there's a learning curve, but not too bad. You have to be careful - if you go too fast through your presentation and you've got too much movement from one spot to another then your audience can get dizzy.
There are many more "flashy" concept mapping tools on the web, but CoMapping is the one I keep returning to. It's easy to use, reliable, and I like the way you can expand and collapse nodes to control the flow of your presentation.