It finally stopped raining long enough for me to mow. I mowed my entire property (3 acres) so I could get an "apples to apples" comparison between the Grasshopper and my Craftsman LT.
Total riding time on the Craftsman was 5.0 hours
Total riding time on the Grasshopper was 2.3 hours
That's a time savings of 54% on my first try with the Grasshopper. I suspect that I can increase that to 60%+ time savings with a little more seat time on the Grasshopper. An hour in the Grasshopper seat is a lot less fatiguing than an hour in the lawn tractor seat as well. I can now mow grass after work on a weekday, as opposed to taking the better part of a Saturday or Sunday. And to boot I am much less fatigued after getting off the Grasshopper.
As far as I could tell, very little of the time difference was due to the difference in cut width between the units (42" for the LT vs 52" for the Grasshopper). It seems that most of the time savings were from 1) being able to mow at full speed without compressing a vertebrae, 2) being able to turn around in under two seconds, 3) being able to cut around trees/obstacle with in a single pass, and 4) being able to mow cross slope.
There are a few disadvantages to the Grasshopper though: 1) I now have a lawnmower payment of $200/month for the next four years and 2) It's takes about 20% more fuel to mow my three acres as compared to the Craftsman (3.5 gallons for the Grasshopper vs 3.0 gallons for the Craftsman). Both are well worth it from my perspective though; I'll gladly pay $7,500 extra (over a nice LT) in equipment costs and $1,000 extra in fuel costs if it saves me 1000 hours (50 hours per year) and a lot of fatigue over the next twenty years (Assuming that an LT would last as long as the Grasshopper, which is highly doubtful since they are so cheaply built and would accumulate twice as many hours mowing the same amount of acreage...)