Slightly related: what many people don't know is that on OS X and BSDs, commands often react to SIGINFO (Ctrl-t), giving progress information. E.g. from the cp man page:
If cp receives a SIGINFO (see the status argument for stty(1)) signal,
the current input and output file and the percentage complete will be
written to the standard output.
As far as I'm aware, Linux tools do react to various signals, just not SIGINFO because it comes from BSD and Linux just doesn't use that particular signal.
You can check dd progress by sending USR1, for example.
You'll need to use ps to get the pid if you've got multiple dd instances running, and you'll of course need to run that as root if your dd instance is running as root.
