The link doesn't work, but I am aware of stumbler. What use would a
cruising
sailor put stumbler to?

I pull into a harbour in the Bahamas, drop the anchor. Once settled, I
turn
on my laptop or pda and look for networks (the wifi card's software allows
this). If there happness to be a hotspot, fine. But if not, what do I
do??
Pull up anchor and motor around until I find one - maybe in another
harbour
20 miles way?

I guess I just don't see how this would be of practical use to someone who
is actually out there sailing.

Have you tried it?

It's useful in seeing not only the available networks but their signal
strength. This can be very useful if you want to position yourself for a
better signal. Or aim an antenna if you're anchored such that it's
practical (as in, not a single hook swinging).

Leave it running on a laptop in reasonable view from the helm and you could
use it to find the most suitable spot to anchor BEFORE throwing out the
hook. Or to make a temporary connection to the net, get what you want and
move on to your anchorage.

It's a tool, like any other, that's useful to those that understand it.