When tracking my milage, I usually count the elliptical. From my HRM, I try to keep my heart rate comparable to my running heart rate. For me, I estimate 20 minutes is 1 mile.
For biking, I NEVER count the mileage... just cause I could maybe 20 miles in an hour where I could never come close walking.
For me, I find it better to track my minutes, not my distance.