The more I think about it, the REAL advantage of the network thing is this: it always seems that the files I need are on the OTHER machine. In the past this meant that I had to find the file on the other machine, copy it to the machine I'm using, (yawn), and then I could use it. After a while, your hard drive starts to fill up with all these extra files and you find yourself frequently trying to clean up your hard drive because of all this extra stuff you've copied over (which are just duplicates of what's already on your other PC).
When the second computer is on a network, you can leave all the files where they are and access them from either PC without any copying. If you do need to copy a file over you can just copy and paste like you do with any other file in Windows Explorer. Also, if you want to make a backup, for example to a CDR, you can drag and drop files from either PC into your burner application, again without copying anything over.
I must admit that I haven't tried all of the USB link software out there so some of these newer utilities may offer similar functionality. However the speed thing with USB is definitely going to be an issue when you're transferring large files like WAV and MP3.
Chris