Yeah we discussed this in another thread and I have one, much like Aaron described but I bought it used, with some extensions, for half price. I have the briggs engine and have had no problem after I drained the old gas.
I wouldn't say it's ONLY useful on steep roofs. I'd use it on any roof where it is long enough, flat or sloped. I prefer my materials ground delivered on sloped roofs but on LARGE flat roofs I prefer a roof top delivery, when possible, and a laddervator when not possible.