I do this; my library is about 80GB (hence my somewhat panicked emails to Dropbox asking for the ability to buy more space). I have two Macs, and the syncing w

I do this; my library is about 80GB (hence my somewhat panicked emails to Dropbox asking for the ability to buy more space). I have two Macs, and the syncing works very reliably -- even when I forget, and start iTunes on my laptop before the little doo-dad tells me that Dropbox is finished syncing, and Things Get Confused, quitting iTunes and waiting for the sync to finish always resolves any issues that come up. Of course, I use multiple iTunes instances serially; may the Prophet Muhammad (صلى الله عليه و اله‎) protect you and intercede on your behalf if you try and run the client on multiple machines simultaneously.