Are your photos still viewable in the Photos app?
I've had the camera "stick" a couple of times on my iPhone 4. I figured it was just a problem not being the new faster chip phone. I've got it back by tapping the Home button once to leave the Camera, then double tap the home button, hold camera icon, press the red close dot and try again.
Maybe you need to power down the phone, power it back up. You know, hold the power button, slide the red slider. Wait for a few seconds after it shuts off, then turn it back on.