180 - 225 miles between regens. Duration of the regen averages 20 miles, and by my rough (very rough) calculations consumes 2 gals of fuel to get the job done.
As perfectly described above the distance between regens will shorten up considerably if you do a lot of idling. I've read that it is less damaging to these engines if you stop and start the engine more frequently rather than allowing to idle.
Yep, I'm also calculating between 1-2 gallons of fuel for a full regen with the lesser amount of fuel used during the hotter summer months on straight freeway. Overall it's looking like a 5-7% impact on fuel economy...more if idling a lot.