This all depends on the traction of your wheels, size of your wheelbase, and CG of your robot.
The problems you're likely to encounter are:
1. Your robot doesn't turn.
2. Your robot bounces like crazy when turning.
3. Your robot draws waaay too much current when turning.
Keep in mind you should test for all these things on carpet, as it has much different properties than bare concrete.
All of these are symptoms of your wheels being forced to slide sideways and not wanting to do so.
This thread has a good discussion on ways around these problems:
http://www.chiefdelphi.com/forums/sh...ad.php?t=24837