Another option I used to do was this:
I had a NAS drive attached to my router. It could be accessed by all PCs.
I setup a family tree folder on there. I setup FTM on all PCs individually. I then used synctoy (microsoft) to make a copy of the FTM files onto the NAS drive.
Each time before I loaded FTM i ran synctoy. It meant each FTM was kept up to date.
A bit clunky, but worked. Dropbox is much better.
BTW synctoy is free: http://download.cnet.com/SyncToy/3000-2248_4-10629009.html