My iPhone 3GS has a problem. When I take photos, video, or screenshots, the Photo Roll shows the count on the Photo Roll icon, but when I click the icon, the media is not inside. When I sync to my computer with iPhoto, all the media shows up. I tried restoring to a previous backup to no avail, but have read that if I restored back in time far enough, I can probably make this problem go away. I wasn’t interested in this so I sought an alternate method and found it!
1. Backup/Sync your phone just-in-case
2. Use a directory browser such as PhoneView or some other tool (Download the trial of PhoneView: http://www.ecamm.com/mac/phoneview/)
3. In PhoneView Browse to the /Disc/DCIM/ folder and delete the entire .MISC folder. (I actually deleted everything in the DCIM folder)
This solved the issue for me without having to resort to a restore. Also, using those programs you can recover any photos/videos that were taken that you could not get to.