Last Wednesday I gave a presentation to the Northeast Ohio Information Security Forum on Maltego which is a fantastic tool for information gathering. The presentation focused on a high level overview of the application and how it can be used for all types of security related work including security assessments, investigations and helping find public information about a company or person.
You can download the presentation here. Like I mentioned at the talk you can get more information on Maltego from the Paterva website. If you are looking for a few good tutorials you can check out part one and part two on Room362.com or Ethicalhacker.net.