Subject GRE is part of the application not the only part. As I told earlier, most of the MGRE questions are available freely. So, lot of people from specific regions usually score very high (> 95). But low MGRE definitely hurts.
I know one person from Brown with MGRE 76 (Engineer, but not from India), one from UMD 85,... few at Cornell between 95 ~ 97. If you apply for Yale, MIT, Harvard,.. if your score is above 800 that's it. If not it might be a concern. But if you look at some middle schools then you have to score >90 (like OSU). But, people never make decisions based on MGRE scores alone or your MGRE never a very important part of your application. However, it is important.
By the way, I know atleast two people at MIT whose MGRE scores are in 700s (ofcourse they are exceptional). When my advisor was in ad com, he told me that if MGRE score is > 800, he will look into that application, if not he won't till the end of first round.