I signed up for a SlideShare.net account yesterday so I can explore if we can use this web app with instructors to help them post their slideshows and documents for their students to access. Before checking further, I thought this was just like the other Slidedeck sharing sites, which are many, but I was pleasantly surprised that you can add an audio narration to the powerpoint slides, if you wish. You do this by uploading a MP3 file with your narration and then adjust your slides to synchronize on the time line. I haven't actually tried this yet but it is very promising.
You can also add other documents to your account and distribute them to others, while tracking the number of accesses.
This is a free service that has a Pro level of server that is a for-fee service. They claim to be the largest sharing site for presentations.
I did notice that they are using Flash technology, which is becoming old and obsolete, especially since Apple mobile devices can not open them.
Check it out at http://slideshare.net.
If you are using this, please share your comments about it.