Fascinated by the concept of packet crafting, I was just scratching my head about "Scapy" for past few days.
http://www.secdev.org/projects/scapy/

I am amazed at how powerful packet crafting can be against Firewall's, IDS and  some Wireless attacks. I was just wondering how often is packet crafting involved in real life pen testing or is there any one who use packet crafting as part of their job??