As others have pointed out, a front-facing camera sounds like a good idea until you think about how you'd have to hold the iPad "just so," so that you'd get the right angle for the picture. It certainly wouldn't work well if you were trying to prop it up in your lap, unless you're going to hunch over to look down at it.
Now if they could come up with a clever solution to that problem, I'd definitely like to see a camera in a future iteration of the iPad.
Let the camera swivel, and make it possible to control from software (throw in face detection, and let it auto-trace your face when you shift the tablet around). It needs some thought, but I'm sure it's not impossible to do well enough for Apple's standards.
Now if they could come up with a clever solution to that problem, I'd definitely like to see a camera in a future iteration of the iPad.