On Private flying there is a thread about a mid-air between a C150 & glider resulting in death of glider pilot. This is not a Mickey mouse issue and deserves more exposure than 'Questions'.
But in which airspace was it? And was either the glider or the C150 flying IFR? If not, it is quite a different discussion. VFR flight does rely on the big sky principle, however even a perfunctory scan of the airspace is nowadays often replaced by constant staring at the iPad in powered VFR flights.