A few years ago I played around with ettercap. It really helped me get to grips with how insecure ethernet can be. It is a great tool to demonstrate Bruce Schneier's points on how SSL on websites is often useless. It also taught me about tools like arpwatch in an effort to defend against mitm attacks.

I noticed that ettercap had released what it called it's next-gen interface and so I thought I should try it out.