Maybe to clarify, plus I do find this a fun topic......it looks like some of you guys are thinking of the term "ATF" as if it means a particular weight or has some other property that either is compatible with the forks inner workings or destructive to them. It doesn't. As a couple of folks have mentioned, fork action is primarily about the weight of the fluid, that's what's going to dictate if it makes your forks feel good for your forks and conditions. Whether it be ATF, fork oil, motor oil, hydraulic oil, whatever, it comes down to the weight. "ATF" if just a convenient label that gets thrown around, but it comes in all different weights just like fork oil. Doesn't mean a whole lot by itself other than it's probably going to be somewhere around 8 cSt at 100C of it's a Dex III equivalent or or 5 if it's the LV variety. No different than your "proper" fork oils coming in 5w, 10w, 15w, whatever.
Back to the OP question of can he use ATF for normal street riding with an avg size rider? Yes, nothing bad will happen. Period. Will it be the best feel? Maybe, it depends on your forks and what you consider "good". You never know until to try it. If the action is too stiff or wallowy, go to a lighter or heavier weight oil. But look at the viscosity specs, the printed weight on the bottle doesn't mean a whole lot unfortunately. M1 ATF is great stuff, I use it in forks and shocks, but it only works great when the viscosity matches up with the above. I can tell you it's almost identical to Honda/Showa SS8, if that appeals to you.