I think this information should be helpful for many people but using DMZ is a LAST RESORT. When this post was first written, the Xbox 360 did not have nearly the amount of applications that it has now. I have a lot of information saved on my Xbox Live account and my console that I want to keep protected, and DMZ leaves the console open to ANY internet packets that are sent its way. It's probably not very likely that you will be "hacked", but there is certainly a greater risk of it these days than in the past.
There is a LOT of information out on the interwebs that can be used to learn more about general networking, NAT settings, and your internet bandwidth and latency. I will start a new thread soon and post some links I have saved that I found particularly helpful, but will mention that the COD website forums and Activision website both have some good general information.