The Filefield module comes with the Filefield-Meta module. This will in conjunction with the GetID3 module grab all sorts of information from your uploaded audio files.
To display e.g. the duration of an uploaded mp3 file simply put the following code into your theme template (e.g. node.tpl.php)

<?php print $field_audiofile[0]['data']['duration']?> secs

Of course you have to name the field after your filefield. (audiofile)
This will ouput the exact seconds of the file.

For those of you not so familiar with hooking directly into the theme there is an even easier way: http://drupal.org/project/dynamicfield

Put a dynamic field into your content-type and write the following code:

$dura = $node->field_audiofile[0]['data']['duration'];
return $dura;

But it gets even better. If you would prefer minutes and seconds, just use this:

$dura = $node->field_audiofile[0]['data']['duration'];
return floor($dura/60).":".($dura%60);

I hope this is of any help for anybody! Enjoy!

Thank you very much xqbzzr!

Building upon your fine examples, ID3 tags are stored in subarray [tags]:

$artist = $node->field_audiofile[0]['data']['tags']['artist'];
return $artist;
$album = $node->field_audiofile[0]['data']['tags']['album'];
return $album;
$songtitle = $node->field_audiofile[0]['data']['tags']['title'];
return $songtitle;
$tracknumber = $node->field_audiofile[0]['data']['tags']['track_number'];
return $tracknumber;
$comments = $node->field_audiofile[0]['data']['tags']['comments'];
return $comments;
$year = $node->field_audiofile[0]['data']['tags']['year'];
return $year;
$genre = $node->field_audiofile[0]['data']['tags']['content_type'];
return $genre;
$composer = $node->field_audiofile[0]['data']['tags']['composer'];
return $composer;

***Another Use: Dynamic Field Tokens:
I wanted to use the ID3 data to generate custom node titles. It seems Dynamic Fields are not exposed as tokens, for use in Automatic Title Generation or similar modules.

This is solvable using the Custom Tokens module. You will utilize the exact same code as above for your custom tokens.

bradspry