I have to agree with dhlizard totally...If you are not auto downloading your photos to Aperture (Mac) or My Pictures (windows) when you plug your iPhone/Camera in then you are messing with disaster.
Have your photos download to a specific folder, select that folder in iTunes and it then puts all those photos right back on your iPhone in a folder, not the camera roll.
According to the iPhone User Guide:
1) Because music, movies, TV shows, podcasts, and photos are managed on your computer, these items are synced one-way, from your computer to iPhone.
2) Syncing Photos from your Computer
If youve turn on syncing, iTunes automatically copies or updates your photo library (or selected albums) from your computer to iPhone whenever you connect iPhone to your computer. iTunes can sync your photos from the following applications: PHOTOS DO NOT SYNC WITH/IN ITUNES like your music, vids or app data.
3) Updating and Restoring iPhone Software
You can use iTunes to update or restore iPod software. You should always update iPhone to use the latest software. You can also restore the software, which puts iPhone back to its original state.
 If you update, the iPhone software is updated but your settings and songs are not affected.
 If you restore, all data is erased from iPhone, including songs, videos, contacts, photos, calendar information, and any other data. All iPhone settings are restored to their original state.
The above is all taken straight from the manual and should explain why all of you have lost your photos. If you are not manually or automatically backing them up to a photo folder then they are not backed up when you sync your iPhone with iTunes. Backing up photos is a seperate operation that is accomplished when you plug your iPhone into your computer and auto save or manual save prior to syncing.
Hope this helps and if your not sure, the manual is free to download in PDF format from Apple.