I am having the same problem with the camera app. I'll be using it and then the screen just goes black. I check other apps and their fine, go back to camera app and still just black. The only way i know to fix it is to reboot the itouch by holding down the power button and the home button for like 5 seconds until the itouch reboots, then the app works again until later when the screen goes black and you have to do it all over again.
Same thing just happened to me, found another solution though.
Plug the USB cable into your PC/base of iPod Touch.
Turn off the iPod completely.
Wait 10 seconds and re-power the iPod.
Now load up the camera; and the screen should be back to normal.
I have similar screen freeze issue with my Sony Erricson K700i Mobile phone, and plugging in the 'power' cable always resolves it, so it would seem to be of the same method used to resolve this iPod issue!!
Strange thing as you've posted, all other apps etc still work. Maybe support will get around to resolving this bug!!