How many miles is too much for a used car?

I'll admit I know nothing about cars. While shopping for used ones, I saw that all the ones in my budget seem to have at least 80,000 to 130,000 miles on them already. But how many miles is too much? I remember hearing before that 100,000 is quite a lot, but I know people who have upwards of 190,000 miles. What would be your mileage limit if YOU bought a used car?