I know of no Live CD that does this.

There are commercial products in the PC world, mainly aimed at Windows users that do this. But your average USB cable does not connect this way, and I don't know if it would even be safe to hack together a cable that just cross connected the wires. I suspect it could cause problems, particularly if the USB supply voltage were just tied together between two different systems. The products that I have seen for transferring files under Windows generally include a special usb adapter cable to try to do this with. And all of the cables are not the same, different software approaches the issue of how to interconnect computers by USB in different ways.

So can it be done? Sure. Should it be done? Maybe not. One needs to decide how to safely connect two USB ports and how the average smuck is going to come up with the magic USB cable to do this. And in the end you still have a hard drive access solution with the well known and hated USB bottleneck.

A much better and cleaner solution would be to connect two computers by ethernet, not USB. Friends don't let friends network with USB. There are many file transfer solutions once you decide to connect two computers through a router or even straight to each other with a cross over cable or auto-sensing NICs (actually you only need one auto-sensing NIC in this case). You could use any common file sharing solution. Personally when I want to transfer a lot of files between systems I like to use a FTP server on one of the systems, and while there is likely a live CD with a FTP server that doesn't require fancy configuration to be minimally operational, I don't know of one. But FTP or samba or some other network based file sharing solution is likely to meet the same needs as a USB based solution, not require any atypical hardware, and be much faster.