In Baroque times, people thought that B minor was the key of passivesuffering. Christian Friedrich Daniel Schubart (1739-1791) said that it was a key that was complaining gently and quietly, something that matches Bach's use of the key in the St. John's Passion. By Beethoven's time, B minor had changed in people's minds: Francesco Galeazzi wrote that B minor was not suitable for music in good taste, and Beethoven labelled a B minor melodic idea in one of his sketchbooks as a "black key". The chord was famously used as the first chord in Pink Floyd's 1979 hit "Comfortably Numb". The second movement of Rodrigo's Concierto de Aranjuez, one of the most famous compositions for the classical guitar, is in B minor.
It is a common key used in rock, folk, country and other guitarist-based styles because a guitar is naturally tuned so that all the open strings are notes in B minor.
↑Michael C. Tusa, "Beethoven's "C-Minor Mood": Some Thoughts on the Structural Implications of Key Choice" in Beethoven Forum 2, Christoph Reynolds, ed. Lincoln: University of Nebraska Press (1993): 2 - 3, n. 5