manually manage photos and videos iPhone

You can manually manage music and videos, but not photos.
Since the iPhone does not support disk mode, there is very little benefit with manually managing music and videos with an iPhone.
If your iPhone is restored with iTunes if wanted or needed, you must remember which songs and videos were manually transferred to your iPhone previously and manually re-transfer the songs and videos. When syncing making use of iTunes playlists for music, your selected iTunes playlist or playlists can be retransferred to your iPhone. After purchasing any music from the iTunes store with your iPHone, the music will be copied to your iTunes library automatically the first time you sync your iPhone with iTunes after doing so. The same applies with apps when having Sync Apps selected under the Apps tab which is a good idea to have selected for a number of reasons.
 MacBook Pro 15" Intel Core 2 Duo/2.53GHz/4GB RAM/500GB HD Mac OS X (10.6.6)  iPod w/Video 30GB,  iPhone 4 32GB

Well I manage my music manually so I can use multiple computers but once I load photos it makes me bound to that PC.
What is disk mode?
Windows XP Pro

You cant manually manage music and video with multiple computers with an iPhone as is possible with most iPods since the iPhone does not support disc mode. Disc mode is what provides for manually managing music and video with multiple computers with iPods that support disk mode.
 MacBook Pro 15" Intel Core 2 Duo/2.53GHz/4GB RAM/500GB HD Mac OS X (10.6.6)  iPod w/Video 30GB,  iPhone 4 32GB