I just got my tire tread checked out by the dealer and i have:

3/32" on the rears
5/32" on the fronts

How many miles do you think I have left on these tires? I have put 23k miles on them (OEM 19" Potenzas).

 

I've got almost 25k and the rears goin bald. they're not down to the cords yet but i'm getting them replaced soon.

 

Taken from About.com:

Q. Dear Sir: How do I tell if the tread on my tires is okay (that is when do I need to change my tires)? I recall there was some quick and dirty way to check by using a dime and then seeing if the tread went to FDR's head (or something like that).

A. You were close. It's not a dime but a penny. If the thread didn't go to the top of Lincoln's head, you needed new tires.

If you want to get technical, if the thread depth goes below 2/32 of an inch, the tire should be replaced. There are also tread wear indicators on tires. Tread wear indicators are molded into the bottom of the tread grooves. When tread depth is 1.6 mm (2/32 inch) , the tread wear indicators will appear as a 13 mm (1/2 inch) band. Tire replacement is necessary when indicators appear in two or more grooves or if localized balding occurs.

 

^+1 on the penny trick

 

You can pick up a tire tread gauge for a few pennies and be totally accurate. Owning a G35 Coupe, I need one and have it in my center console.