I painted my 2-car garage floor about a year ago. I used a good quality grey garage floor paint, with a sand additive to increase traction, and let me tell you I am paying for a lack of surface preparation. I basically swept, vacuumed and mopped, that's it. No acid wash.
The paint has bubbled and flaked-off in numerous areas, and the family and I are constantly bringing small flakes into the house on our shoes. Not to mention that we're graced by patches where you can see the green paint underneath.
Take it from me, invest the time and money to prepare the surface properly (see other links in this post.) Also, I would highly recommend a better-quality covering like something rubber or epoxy based.
There are even more expensive solutions than the Home Depot / Lowe's do-it-yourself jobs, I think there are even services that will come and lay down expensive coatings for you.
Don't skimp on the preparation or the materials. You want to do this only one time and have it last and look good. It will have to live up to vehicle use, standing water, (in my case) snow/ice/salt, and all the other abuses that a garage floor will have to withstand.
Just my $0.02
