I've had a look at the fping sources.
There aren't any really obvious reasons why it should take so long.
If you run it with "time", it also claims that the user- and system-time
are really low (I tried with ~1500 hosts), but the wall-clock time is
like 90 seconds (default options). Which kind of points at the code not really doing parallel pings.
I think I'll try some modifications to it over the week-end. If any of
it seems to improve it, I'll let you know.
I gave the source a quick peruse before sending my initial email, and
my gut was telling me likewise. Thanks for looking in to it :)
-Eric