Keithr, cable break-in is no joke. Some people have measured differences between identical cables where one was broken in and the other wasn't, although the equipment and the knowledge needed to do so are costly and substantial, respectively, which is one reason why the results haven't been circulated.
Depending upon materials and construction, break-in can take several hundred hours. For example, the TG Audio cables I sell take 30 days (720 hours) and sometimes a bit more to break in. TG is probably the only manufacturer who breaks in all interconnects and speaker cables, which benefits the customer. TG uses silver conductors. Others use copper or other materials, and break-in time varies.
I don't expect anyone to believe the above, but my customers and my own ears verify it. As a service I offer break-in of any interconnects people want, your choice of five days or thirty days - your only cost is shipping both ways and one your best live CDs per set.
Brian