Information Rights Management in MOSS
Based on the number of questions I see in the newsgroups and forums regarding Information Rights Management (IRM) I figure a quick overview post is in order.
Most people know that IRM allows you to setup rules that determines how long a document is considered viable and what to do with it when it expires. However there are other features of IRM that are as useful as well. Other features that are part of IRM include Labels, Auditing, and Barcodes.
Labels allow you to add important information to a document when it gets printed. You can allow users to enter the label when the document is uploaded and you can set what the lable will contain. You can use most of the metadata that is associated with the document and use it as a label. Just surround the metadata with {}. Interesting tidbit. The example that is listed on the page uses pieces of metadata that does not exist in most document libraries. 
This seems to require the Rights Management Server to work correctly.
Auditing is the feature I find that I use the most. In these days of lawsuits and multiple stories of cover-ups, auditing can be very useful. You can keep track of who opens. edits. checks in/out, moves/copies, or deletes/restores the document.
Finally barcodes works like labels in that they get printed with the document. This seems to require the Rights Management Server to work correctly.
Administrators can also make these available or unavailable through the Central Administration.
Well, there is it....an incredibly brief intro to IRM. I think you will find that most people will use the expiration and auditing features the most since they work with very little effort but the other features can be quite useful as well.