OK everyone. Others have mentioned th "/DCIM/.Misc folder solution" and I just wanted to point out that it also worked for me too.
Backstory: I've been having this problem for about 2 months. The same thing as everyone. After a big sync the problem started. The phone won't save the pictures. you just get a white outline where the picture would be and it will disappear entirely when you try to view it.
This is NOT a problem with your actual phone hardware. Exchanging phones at the apple store won't do anything.
There are workarounds discussed in other threads that will work temporarily but not permanently. I tried backing up and restoring multiple times. for instance the backup and restore but stop in the middle of the restore and take a picture method will work for a bit but not for long. You may have the same problem again soon.
I've found that the fastest and easiest way to fix this is to go in and delete the hidden .Misc folder from the phone. You don't need to restore or any of that jazz.
1. Backup/Sync your phone just-in-case i guess.
2. Download the trial of PhoneView:
http://www.ecamm.com/mac/phoneview/ (there's other methods and programs you can use to go in and view & delete that folder but i didn't explore them.)
3. Launch PhoneView and in its preferences enable (Advanced Disc Mode)
4. In PhoneView Browse to the /Disc/DCIM/ folder and delete the entire .MISC folder.
That's it.