I’ve known about the presence of audio files in Lightroom 1.1 for a little bit now, but as I don’t own a camera that can import them, I not investigated it much. Ian Lyons on the other hand, does and has. Due to his practice of converting files to DNG and deleting the audio, he only recently discovered that you can, in fact, hear audio files created to go with your images. These voice annotations are treated as sidecar files and can be accessed by clicking on the arrow beside the name.
More information can be found in Ian’s post on them, along with an expansion of information on GPS in Lightroom.
Update: I see that James Duncan Davidson has also posted about this over at the O’Reilly Inside Lightroom Blog