The film was released without any expectations for it to bring a lot of money. But the film got extremely popular with USSR citizens and became one of the highest grossing films in the USSR history of movie-making.
For the disco club scene two real Russian bands were invited to play, "Arax" and "Mashina Vremeny" both extremely popular back then. Information leaked to the public and set was overcrowded by both bands' fans to listen for their music and eventually provide mass dancing background free of charge for the film makers, completely unexpected.
Starting with the comedy "Don't Cry!", the credits of the director's films include a certain Rene Khobua who was involved in the episodes, but there was no real actor with that name. In reality, Rene Khobua was a Georgian builder whom Georgiy Danelia and Rezo Gabriadze met in a hotel while working on the film. They tried to "test" their script on him, while at the same time taking him to feasts with friends. Khobua listened to them obediently until it became clear that he did not know Russian well (the script was written in Russian), but out of politeness he did not mention this and simply praised everything that Gabriadze and Danelia wrote. Gabriadze suggested inserting Khobua's name into the credits of the film, and thereby thank the builder.
From Wikipedia.