I live in the area (two streets away) and I walk to the 46th street stop (entrance on 48th). I have one friend who has lived in BVG for roughly 5 years. She has been happy there. For 6 or 7 years prior to that, she lived on 62nd (If I remember correctly) one block north of Northern Blvd. She has always liked this hood. I've lived here for 3 years and I always feel safe, but I also use common sense wherever I live.
You should still check with the authorities as the other two posters suggest, but I can offer one anecdote. I know two young women who were mugged nearby. They are very bright young girls, but one morning around 3 or 4 am they were ,by their own admission, stumbling home. They were physically assaulted and robbed. No weapons were used, but they were both hit, one in the face. It was a truly traumatic experience and I felt horrible for them. It also hurt to know that such a thing happened so close to my home. They have both understandably decided to move, but after some reflection, I realized that it could have happened anywhere in this (or any other) city. I still love this neighborhood blemishes and all.
All that having been said, if I were coming home to BVG from the R late at night I would get off at the 46th stop and walk the few extra blocks rather than come from Northern. Mostly because I know those streets, but also because that route has more multi and single family homes. People tend to loiter around the businesses on Northern and around the grounds of the public housing on 50th, not around the schools and on the more "residential" streets.