Tom Besser;
>I assume this may be breeding season behaviour?

I think so. The pair I'm most familiar with in the Blue Mountains
tend to be found fairly high off the ground in nesting season. They
prefer to nest 40-50 feet off the ground, as I understand it. They're
largely silent during other parts of the year, and their call is deep
and resonant, which is one reason you have difficulty pinning them down.
Higher-pitched tones are easier to locate. This is not only true of
people and sound, but of any wave-like source. A shorter ("higher", one
might say) wavelength allows more precise location, other factors being
equal (which is why IC manufacturers use UV light sources rather than
sunset-colored ones).

In winter, though, wherever they occur you hear of great-gray owls
perching low, and being approachable.

One of my favorite books is a book on great-grey owl banding. Those
of you who know me as a raptor bander can understand. These researchers
banding wintering great-grays in Canada had a fantastic capture technique.
There were two of them. One used a fishing pole with a block of wood
painted gray and a pipe-stem made black (that's a mouse, folks). The
other had a fishing net, ala those used to snag steelhead and the like.

Cast the wood/mouse lure towards an owl perched on a short fir. Owl
grabs (this is all in deep snow). Use fishing pole/spinner to wind
in the lure with owl attached. When the owl is literally at your feet,
the guy standing next to you with the fishing net traps it.

The book has many pictures detailing the methodology, it's a hard-to-locate
hoot. (bad owl pun - sorry those of you who want the list to be strictly
about birding - but it's true. It's a hoot, and hard-to-locate because
it's out of print).

I'm surprised that this particular owl isn't riding on the horn of
some equestrian's saddle at this point :)