When filling IFR, there are two boxes you put numbers in, AIRSPEED and
TIME ENROUTE.

These go back to the old days, but are still applicable today.
AIRSPEED, as the name implies, tells ATC how fast your airplane is
going through the air.
TIME ENROUTE tells ATC when to expect you at your destination.

One of the regs says that you have to advice ATC of any airspeed
deviations of +/- 10% (someone correct me if I am wrong, I do not have
the AIM in front of me).
However, the TIME ENROUTE should take into account headwinds and/or
tailwinds. This is important in the event of loss of comm.

Here is the question:
When you fill in the AIRSPEED box, do you give the actual indicated
airspeed for your cruise power setting?
Or, do you use the "groundspeed", based on winds aloft?

If you use the actual indicated airspeed, the math is not correct for
the time enroute.

If you use the actual airspeed and the calculated no-wind time enroute,
you mess up the system in the event of loss of comm, since you will not
be where they expect you in the elapsed time.

Further, in these days of RADAR, LORAN and GPS, do you advice ATC of
the groundspeed deviation from the airspeed?