Prezi reminds me very much of PowerPoint, but I find the controls to be a bit confusing. I believe if I were to play with it long enough that I would be able to control things better. One nice feature of having the presentation online is not having to carry a thumbdrive or have a certain computer that has software such as PowerPoint loaded to it. I had a thumb drive stolen from my laptop at school one year and it was never returned. However there are also downsides to having a presentation online as well. Our school sometimes has internet outages which are outside of our control and sometimes and it can be out for several days. This would leave me without a way to present my work to others if we were to have one of those happen. Also our school has been having some power outages as well and I would be afraid to lose my work if it the online program was not saving periodically. If I would using PowerPoint I could at least save it to my drive before the computer would have to be shut off since we do have battery backups connected to the computers which allow them to stay on for a little while. There are lots of tutorials and lessons available to help you with your Prezi presentation, that is very helpful. The most basi free version does not offer as many features as those you have to pay for. Also with the free version the storage is only 100MB. The enjoy version for $59 a year gives you 500MB a year allows you to make them private and use your own logo and the pro version for $159 a year gives you 2000MB storage and the ability to work offline. One nice this is that students and educators can receive the enjoy for free and the pro for only $59 a year. Overall it looks like an interesting online program, would just take a little getting used to the wheel that is used to design the pages.
Mybrainshark allows you to upload PowerPoints and then add voice. You can insert poll and surveys. You can share the presentation on facebook or other places including Youtube video. You can upload videos as well. You can add background music to a presentation. I think a tool like this would be nice to have if students missed a day of class. You could add the notes or other things you discussed during the various slides and they could view it at home or upon returning to class. Again the basic service is free. For the Pro 1 version it is $9.99 a month and allows you to identify viewers, share presentations privately, add passwords for security, and improve analysis with detailed view and reporting alerts. To me this seems little bit simpler since you can upload a premade PowerPoint and then enhance it with other things. Another great tool to use and since it can be embedded on websites something very useful for a teacher to use.