All the pingboot modes attempt to reduce the latency caused by the server.
The default implementation adds around 20msec to each players ping (under linux).

Mode "1" reduces this by using a different wait method (a select() call).
This method reduces the latency to 10msec.

Mode "2" uses a similar but slightly different method (and alarm() type call).
Again, the result it 10msec worth of latency being added. NOTE that this method
has the potential to hang a server in certain (terminal) situations.
If anyone has used this mode recently (not the first test we did!)
and it hangs please speak up

Mode "3" minimises the latency to the minimum possible level by processing
a frame EVERY time a packet arrives. This causes the lowest possible latency,
but can also cause extreme CPU usages (it does a complete frame for every packet,
with each player sending lots of packets per second and 30 players
this adds up to insane amounts of frames). Use this mode at your own risk,
it will consume all available CPU, don't complain that cstrike uses too much CPU
if you use this mode :-)