The difference between the Runnable and Callable interfaces in Java

What is the difference between using the Runnable and Callable interfaces when designing a concurrent thread in Java, why would you choose one over the other?

See explanation here.

The Callable interface is similar to
Runnable, in that both are designed
for classes whose instances are
potentially executed by another
thread. A Runnable, however, does not
return a result and cannot throw a
checked exception.