I fired up the Google machine to answer this very same question for the very same reason. Between some of the different responses, this is what I gathered:
The original Geolandar MT tended to wear more quickly than was optimal in hot weather and/or high speeds due to a very soft compound. The MT+, which I think is the current version, supposedly addressed these concerns with a slightly different tire compound designed to provide better wear characteristics.
From that I drew the conclusion that, while improved, the Geolandar is not likely to be a high mileage tire for that reason and because it is a directional tread pattern. I guess some folks don't rotate tires the way I do, but I go in this order: spare-back right-front right-back left-front left-spare. Obviously that won't work with a directional tread. Additionally, which way do I get the spare mounted? If I mount the spare for the right side and blow a tire on the left side my spare will now mount up in the wrong direction.
The Geolandar seems like a decently performing tire - I'm just not sure it's the right tire for a more casual rig like mine.