In the second Oberwolfach meeting on Complexity Theory, held in November 1974 (see report), Volker Strassen discussed his recently invented randomized primality test with participants. Consequently, a bet (see the original german text) was waged between Volker Strassen and Ernst Specker regarding the conjecture that Primes are in P. Strassen bet that a proof of the latter conjecture will be published by November 1st 1984, and lost the bet by a margin of almost two decades... (In accordance to the conditions stipulated in the bet, Volker invited Ernst to a ballon trip.)
See History of the Oberwolfach meeting on Complexity and Oded Goldreich's homepage.