AudioBoo is okay, but it only does 5 minutes of audio (on my iPod touch anyway), then you need to upload it, then you can do another 5m and so on.

With an iPhone / iPod touch, it's much better to just use the voice memos function, then transfer it back to iTunes and convert and upload that file.

Or if you are presenting from a Mac laptop, plug the iPhone headset into the headphone port and record it with QuickTime7 (you can get a LAME MP3 plugin for QT7 so you can save it out as MP3) or Audacity or whatever.

A video upload site that is a bit easier to get on with than is The nice thing is they'll transcode your video (including HD) into Flash and downloadable MP4, QuickTime and a bunch of other formats.