Most of my trips have been 55-60mpg, but my wife drives the car as much as I do, and she typically parks it with around 40-44mpg on the FCD - together we're averaging around 50mpg when I fill up.
I've noticed on a few longer trips that the engine will (rarely) spasm and vibrate badly when driving on the highway, and that pushing the pedal down or letting off the gas makes it go away, much like what I'd do to exit lean burn in my Insight. Add to that, I have not yet seen lean burn engage in this car, so I suspect it's trying to go into lean burn, and failing.
So, I decided to soak the EGR valve with some WD-40, and clean out the EGR passages:
The passages weren't all that bad and there's no way to know if the valve was causing the problem. I do a lot of driving in the mountains, and temperatures have been below freezing, leaving little opportunity for lean burn, so it might be a few days before I have opportunity to find out if cleaning the valve and passages did anything, but it certainly can't hurt.
Now that I'm thinking about it, I might want to check to make sure the car has the right spark plugs.