Today I was talking to a member of the site on the phone who was using mp3 files to distribute recordings he had created.
Mp3 is a great format but if your intended audience has access to an Apple device like an iPhone, iPod or iPad or even a computer running iTunes then it might be better to send your intended audience our Audio Book formatted files.
This type of file when used in iTunes or any iOS device like an iPhone,iPad or iPod will remember the last position the recording was at and start from that point when you next listen to the recording.
This is the format I use to listen to all of the long format recordings I use SpokenText to create. One other option is to download the recording from your SpokenText podcast URL and then access it via the podcast section of your device or iTunes. When accessed this way the recording will remember its last position.
I have found that either of these two options are best when listening to long format recordings.