Currently coming to the end of this book (yes I know I have been reading a lot recently, but I have a huge backlog of books to get through!), and I can honestly say it is one of the most interesting subjects that I have read about for ages! I can see some immediate and obvious uses for AOP on the project that I am currently working on (and on projects that I have worked on in the past!)
AOP attempts to address concerns that cut across an entire application, examples of this are logging, persistence and security. By defining aspects to deal with these areas, your business code can remain clean and unpolluted.
I would really encourage anyone who hasn't already to read this book to read it soon (or at least read around AOP)!