If you’re one of those people with hundreds of gigabytes of music on their computer and you’re getting sick of swapping over tracks on your iPhone, then maybe it’s time to take a look at a service like Dot.Tunes.  It’s a web server that publishes your entire iTunes library online, so that anybody with the right password (I’m assuming for legal reasons that would be you and only you!) can access them from wherever there’s internet access.  Give them twenty bucks and you can have a custom iPhone interface making searches, playback and playlist management easy.