In his paper Taking advantage of Ext3 journaling file system in a forensic investigation Gregorio Narváez describes the journal of the ext3 filesystem.
Information recorded in the journal helps to recover deleted files. Also the data enables an examiner to build a detailed timeline of events. Inodes tell only the last modification and the last access time. The file system's journal, however, can store many of these events for a single file.
13/12/2007: Changed the link. Hopefully the new one will last a bit longer. Thanks to Sebastien for the hint!
Here's the good link for the paper:
http://www.sans.org/reading_room/whitepapers/forensics/2011.php
Sebastien