I did mine 3 x with a 1 to 1 mix of muriatic acid. It should definatly change the feel of you cement. I think they say like 80-100 grit sand paper or something like that. I used 5 gallons of acid for 700 square ft.
I had brand new concrete and used a dual-head grinder for mine. Worked great, no etching required. But that is clean virgin concrete. No stains, oil, sealer, etc.
My concrete is about 2 years old. I used about a gallon of muriatic acid each time I etched about 150-175 square feet. I didn't add any water to it but I made sure the floor was nice and wet so it probably was about a 1:1 mix. I had to etch twice to get the texture I was looking for.