I brought an M$ force feedback joystick about a year ago, with the intension of using it with stuff like pd (and the odd game). I haven't really used it a great deal since then, although I am still interested in doing so. I'm running windows, so if I were to implement anything, it would probably be directX flavoured... Might get linux up and running on my machine at some point. I don't have any real programming experience, although I might start dipping my toes in.
The SDK's I've seen for forcefeedback, and the literature on programming it, has always worked in terms of playing back specific "effects", like samples, rather than just generally having direct dynamic control of forces in x and y. I might be missing something... Anyway, I guess in practical terms of pd externals, we're probably going to need quite seperate solutions. I don't know if the way immersion devices communicate is different from microsoft, but clearly windows and mac os are going to be different.
Good to hear of someone who's doing this.
Peter