I have been using Prezi off and on for a few years. One of the features that Prezi has lacked until now is the ability to put a voice narration on your presentation. There are plenty of ways to do this with slideshows made with other tools and you could actually do it with Prezi but it was not easy because you had to stick the sound file into a SWF file and post it to your Prezi canvas like a flash object. Not any more.
Two recent added features make this much easier to do. Now you can insert MP3 sound files into your Prezi as voice over narration or even as background music. Voice overs are attached to the steps on your path so in a way, this is using the traditional slide show metaphor. This works great though, you just need to have an MP3 file for each step in your presentation path. The MP3 files can be created with Audacity or any other audio recording application that can export to MP3 format. Most mobile devices have apps available that can do this, so you can even use your smart phone to record your voice overs.
Adding background music is even easier because you can only have one MP3 file loaded as the background music. So if you wanted to have multiple songs in the background you would need to knit them together into one MP3 file before inserting it. Again, you could use Audacity to build this file.
One nice feature is that the background music will automatically scale its volume down when a voice-over file is playing.
Of course you MP3 files will eat up your storage space quota on Prezi so watch out for that.
This new feature can make Prezi much more useful as a online lecture presentation tool for teaching purposes and the price is still free for educators and students. Unfortunately, it is still Flash based but the Prezi app for iOS helps make it playable on iOS devices. I hope they come out with Prezi app for Android devices as the latest ones don't support Flash either.