2003: "IDSs [intrusion detection systems] have failed to provide value relative to its costs and will be obsolete by 2005." (Gartner, "Gartner Information Security Hype Cycle Declares Intrusion Detection Systems a Market Failure")
2008: "Our adversaries are very adept at hiding attacks in normal traffic. The only true way to protect our networks is to have an intrusion detection system." (Robert Jamison, Under Secretary of the National Protection and Programs Directorate at DHS)
I will have more to say about this in a future Snort Report.