I've always found order of magnitude useful primarily as a tool for discriminating between what makes a damn bit of difference and what doesn't. Context is important, but generally anything within 3-4 orders makes a difference, while anything more doesn't.
Also, I had an Astro post-doc who challenged his students to contemplate high-magnitude units, to see if they can actually fit in your brain. The one I recall best is Cubic Megaparsec. People who talk about the distribution of galaxies in the universe toss that term around a bit, bit that volume of space is staggeringly huge. (A parsec is 3.26 light years, IIRC.)
Nice-- google calculator can handle cubic megaparsecs: "one (cubic megaParsec) = 2.93800656 × 10^67 cubic meters"
--LAN3 Wed Sep 7 04:27:24 2005
For some reason I'm more amused by gallons...it's around 7.76 x 10^69 US gallons.
That would be a great deal of milk.
But we're up to the challenge!
"First, we assume a spherical cow..."
--Kirk Wed Sep 7 11:48:01 2005