I'll second that. There is a picture of "accelerated action" on Steinway's web site. All it is, is a rounded balance rail bearing. My piano technician says it is just a gimmick. My 1910 Steinway K does not have it, and the action sure feels exactly the same to me as a new K-52. (Caveat: the action design of the original "K" is not the same as the modern "K-52").
Here is a quote of interest I found via a Google search:
"Steinway pianos are the beneficiaries of a group of patents called "Accelerated Action." The most salient aspect of Accelerated Action is the rounded balance rail bearing, which is in the shape of a semicircle. On other pianos, this part is composed of a compact pile of cardboard and felt circles (creating an upright cylinder shape). Steinway claims that the semicircle construction creates a situation in which the key is more inclined to return to rest position, making repetitions easier for the pianist. Whether or not it really makes a difference is questionable-- when I asked technicians about it, their initial reaction was always something akin to a scoff."
St. Louis, MO
1910 Steinway Model K