Everything I've read (or heard on click and clack) says:

For short term, lower speed use, it's ok. Don't take any 1000 mile trips on the highway doing it. That's why many cars with the mini-spare have a big warning on them that says 45mph max speed. You just spin the spider gears more, like when you're going around a corner and the outer wheel has to travel farther than the inner wheel.

Caveat: Don't do with locked axles. Think of taking a corner on dry pavement with locked axles--chirp, chirp, chirp! as the inner wheel tries to catch up with the outer wheel.