Yet another significant Nexus 4 bug has emerged over at the Issues section of the Android project page, this one relating to the camera. Apparently, under some conditions (several days of being powered on, or taking a low-light shot with flash), the Nexus 4's camera app simply won't capture images anymore. Rebooting resolves the problem, but obviously a problem like this could ruin an opportunity for a candid snap or otherwise quick photo-op, since rebooting will obviously take some time to accomplish.
Another fix that some users have reported works is switching to camcorder mode, recording one second or so of video, and then switching back to camera mode.
The bug also sometimes causes the camera flash to get "stuck" on (if you have flash enabled), which is certainly a nuisance.
The thread currently has 185 stars, and dates back to December 5th.