I take a great personal interest in what are classified as "Man In The Middle" (MITM) attacks. First they are one of the hardest forms of surveillance to detect.
Second, they are much more common than most people believe and used by malicious (sometimes misguided) individuals, corporations and numerous criminal organizations to gather information.
Third, even if detected, the perps can simply close up shop and walk away, leaving little if any forensic evidence.
This means the best defense is detection of the attack prior to sharing information over the compromised connection.
So, let us—in the spirit of crowd-sourcing—share information on MITM here.