to be honest i would not recommend using dropbox for this purpose - presumably you are using a shared folder, which we have found to create various problems as the locking of files is rather unreliable... i.e. you might find duplicates copies and file corruptions.
regarding the changing library folder you are comparing apples with... well PCs - to be more specific two completely different file systems, that use different file paths. arguably though you could only use the embedded library - ubnless of course you need the same objects in other files?
agree that using a teamwork server is pretty much the way to go in this scenario - although it really depends on the bandwidth at both ends...