It's beyond me why the iPhone & iTunes don't support sync'ing from multiple computers. Jason Snell has a good video post that proves it is possible to do multiple machine sync; but it is brutally painful. You basically wind up deleting and re-syncing everything on your phone each time you want to update just a portion.
My music is managed/stored on one machine, and my photos and video are managed/stored on another. To make matters worse, there are times when I just want to move a single song/video/picture onto the phone (what a concept!) and I have to blow everything away (again, because of my multi machine sync needs) to get that done.
I'm surprised that the leader in sync'ing (Apple) machines/online accounts has fallen so flat when it comes to sync'ing their most important device.