on OSX, and ubuntu 12.04, with the beta release, I ran:

$ while true
     echo hi
     sleep 2
  end

After a few iterations, I pressed ctrl+c to interrupt the loop, then pressed ctrl+c repeatedly, even holding it down

The child process was reliably terminated, but never the loop

Eventually, I had to kill the fish process from another terminal

In Bash on Linux:
`while true; do sleep 1; echo hi; done``
handles keyboard interrupts as expected