Originally Posted By: Dignan
The only thing I'm worried about at this point is whether both instances of iTunes can be open at the same time, and what would happen if I added music using either machine with both open. Fortunately there's never a reason that needs to happen, but it might accidentally if one of us forgets to close it on our computer.

I'd make sure to backup the library files from time to time, just to make sure nothing bad happens. iTunes writes to it quite a bit, due to the music count and last played tracking. Also, you can turn on music sharing more as a reminder that the other instance is on. If you see something under "Shared", it's time to go close down the iTunes instance on the other machine. This will require the Bonjour service to be kept on though.