For the more than two years I've been using RTAI in "real", albeit research, control systems. An old small system ran 12 axis on a PIII 350MHz box. The current system has 48 channels (of which only about 42 motors are currently attached/enabled/used) on a dual pIII 1.2GHz box. This includes a 2KHz servo loop, an involved hard real-time path planner, a significant GUI interface, other assorted digital and analog control inputs, etc. The servo loop typically takes about 2/3 of one processor, the planner takes about about 1/2 of the other. I happily use emacs, and browse the web, and compile, and ... while running the control system. One box, no DSPs, no smarts in the drives, ... and very few problems.