IF you want to put it down right, count on the garage/shop being out of comission for maybe a week or so. With all the cleaning and degreasign you'll be doing, you want the floor to have plenty of time to dry, inside and out. It only takes a few hours to do an average sized garage, and the cure time isn't too terribly long, and the smell (from what I remember) wasn't bad.
I've used epoxy floor coverings in industrial applications and it has held up really well, even in the REALLY high traffic foot areas. It has peeled and bubbled up in some locations because the floor wasn't oil/grase/water free, which given the location it was put down, is near impossible.