I don't know what to tell you. I've had the same iTunes library across multiple Macs since 2003, so it is possible. I even have the "date added" and all that kind of metadata intact. Sometimes I accidentally delete a song or a playlist, because I don't pay attention to what's highlighted. Just keep backups and you should be able to recover. Also, remember that iTunes keeps two library files, one XML and one data. You can always regenerate the data from the XML. The idea is that XML is a "standard" and it's written to when iTunes closes. But the data is the working file. If you launch iTunes when the XML is present but the data isn't, it'll regenerate the data file. Sometimes this fixes things.
I wonder what Mark Robinson has to say about this. I'll be sure to ask him at Washington DC 7/10 - Unrest.