It would be great if the 64 bit release of jruby shipped with an actual 64-bit executable.
There is an issue with the current 64-bit setup specific to the ansicon utility for Windows (ansi console colors). The utility works for both 64 and 32-bit machines. However, it does not work with 64-bit jruby. The utility injects into the 64-bit command prompt, which then injects into the 32-bit jruby.exe. But because jruby.exe (32) then launches 64-bit JVM, the ansicon utility is stuck at 32 bit (because of the 32-bit jruby.exe) so it is unable to inject into the JVM.