My experience is that impromptu mentoring has essentially gone away and only concerted efforts remain. When I was stuck on a problem or just needed a break I used to walk around the software lab and look for someone who looked frustrated and then try to solve their problem. Obviously I don't do that anymore. Instead I do have (probably not enough) screen sharing work sessions with other engineers when there is a problem that one of us needs to talk through. It is a good opportunity to learn about how others work and get some work done.