I got one of the Shays the day before Christmas. I wasn't planning to get one because I don't do that kind of "railroading," but it only takes a few moments' weakness to reserve one. (Also, though, I'm inclined to buy almost any steam engine that gets manufactured, if nothing else, to reward the company for expanding our horizons.)
I'm pretty happy with my Shay. It runs smoothly, quite well at slow speeds.
Reading this thread, I decided to see what it would pull on a grade. I have one route on my layout that most of my locos bypass, because on the steep side it has a grade that is 1200 scale feet long and 3.5%, with a slight curve 1/2 way up. When I have a loco go up this grade, I don't want to throttle it to get over---I want a reasonable level speed and still surmount the grade (at obviously a slower speed).
My wonderful Bachmann 2-8-0s can do this grade with up to 15 cars, and 12 cars with perfect ease. So I wondered about the Shay. I don't have any log cars (yet) so I hooked it up with eight Atlas 33 foot hoppers, 5 with MT trucks and 3 with (the new) Atlas trucks. The Shay went around the level stretches at a slow speed and conquered the grade at a creep, but with no trouble (and no throttle increase, either). I added two Micro-Trains hoppers to the train and it slipped, took one of them off, and it was OK. In fact, if the grade was only half the length, the results would have been better, because it had gotten a bit more than 1/2 way through when it lost traction.
So my results: 3.5% grade w/slight curve in middle, 1200 ft. total length, the Shay could pull nine cars. Not bad!