I am by far no expert with the tool but I am aware of the many uses aside from basic network mapping and port scanning.  If you are ever curious as to what more it can do, take a look through the scripts directory on your install.  There are a ton of useful things in there.  On in particular that caught my eye was a script designed to listen for Dropbox.com broadcasts.  Even though you may block the site in your web filters, the client itself goes over a different port that may be allowed out of the network.  Want to find those troublesome folks, well fire up the listener script with your LAN range and this will pick up on the traffic and even enumerate the system broadcasting it.  

There are a number of other useful ones as well.  Just something I thought I would pass on for those wondering just how useful NMAP can be and are new to the business.  Hope it helps.

Oh and before you go wild with running these scripts against targets, check the code first it will tell you if it is a safe one or intrusive.  So if you feel the need to experiment on a production network with security tools in place, you may anger them.  And No I did not learn that the hardway though I was curious ;-)

Thanks, I have a nice nmap book at home I just haven't had the time to go through since the reading list continues to grow.  Might be a winter activity.  I just like that it is just so much more than a port scanner and it is always a tool I load on a new build before I bother with any others.

I finished reading "Nmap Network Scanning" book last month and now I'm practicing the techniques.
It is nicely laid out, this book is beyond just the usage of command line flags, at some places the author gets deep into usage of nmap along with tools like 'DIG'. to make it short, this book is what every book on security tools should be laid out like.

Another good book on nmap I can think of is :
Secrets of Network Cartography: A Comprehensive Guide to Nmap

and if you just want a kick start with nmap, consider reading:
Nmap-Cookbook-Fat-free-Network-Scanning

But by best bet will be Fyodor's book, no other book on nmap(or other security tools) can be compared with the quality of Fyodor's book.