The Bamboo Project report on the fact that Slideshare now supports audio files. Looking at the home page, I think that you have to have an MP3 file of the audio – and then match them. Not sure if you can upload a Powerpoint that has the audio embedded in it.
I think that it will be useful – as it’s often quite hard to work out what should have gone with particular slides – especially when people are sticking to the policy of not having too much text on slides.