About that "#!/usr/bin/env bash" business - are there any systems out there that have "/usr/bin/env", but do not have "/bin/bash"?
Ah, got it. Another failure mode. There is a /bin/bash, but it's an ancient, crummy thing, that is difficult to upgrade. MacOSX does this, so users paper this over by installing a private copy as ~/bin/bash. Thank you.