Like eddie: I too use Orvis backing.
I use the Orvis High-Capacity Gel-spun backing.
Not because of big fish, its for insurance. Like many others, fly line is not cheap!
If the backing fails to do its job, kiss $52+ dollars good-bye.
I have yet to experience a fish taking my line to the backing. The monster pike I caught didn't make long runs.
Looking forward to my first steelhead trip this fall.
Maybe then, I'll think of the backing as something more than holding my fly-line to the real.