Well The only comparison I've done between the two so far has the GPSmap looking more accurate, or at least more consistent than the I-Blue.

Having feedback other than three LEDs and being able to mark waypoints without lugging my netbook with me are big improvements. You'd think Transsystem could have at least put a waypoint button on the 757.

Yes, but this was with the GPX layer in question selected, and it produced an error message.