I had to restore all my files a couple of months ago and when I went to sync my iphone and ipod I got a message saying the devices were previously synced with another library and if I synced with my current library all files would be lost. As it was essentially the same library, it wasn't a problem but I guess if you sync with 2 different computers, all info will be changed to match whichever computer you are syncing with. As far as I'm aware, the same situation would arise using two different accounts. Hope this helps.
