I have a 2006 coupe. The oil change place has told me that I have less than 10% of my brakes left. I'm at 56k on my car now. They're still the original ones.

Also, they tell me that my belts are cracked and need to be replaced. How many miles do they usually last?

 

You got a lot out of your brakes, so you are OK here.
Belt wear is not related to mileage only, but to enviroment and time. They will rot even if car just sits on the driveway.I had mine replaced much earlier than 56K miles.

 

I have a 06 as well but with 25K miles. They told me at my last oil change that I need to get my belts changed too. But my brakes are still good.

 

normally belts need to be changed around 30k. and brakes are normally 30-40k unless you have an 03-04 which is like 20k lol.