Think about the following scenario:

Studios put up some machines to the Net, with high-bandwidth access, and with Xolox installed. Soon they'll be able to find their own movies shared. Create a crippled version of the movie that won't play properly, but make the first few minutes OK - for a short intro peek it will look all right. Exactly the same name and same length as the shared one they found, of course.

Xolox downloads files from many sites if found at more than one sites, based on an exact filename and file length matches. Soon the crippled file will provide download source for parts of downloads here and there. After a while pieces of the crippled file will appear in downloaded copies everywhere that will be shared again and downloaded along with the crippled part - and soon enough there'll be no proper copy of the file anywhere, or at least no one will be able to tell if it's a good one or has pieces of the crippled.
If Xolox does more matching than that, for example a CRC check to compare the identity of two files that looks similar (by name and length), then the above scheme will not work, thank God! If not, here's a place where it could be further developed for our good.

The Xolox community might have quite a hard time to find those hosts and disable access there, say, by a personal firewall. Also studios can easily change their IP... Personal firewalls could be used to control access that Xolox would be able to download only from specified sources, from those with certified good copies - but this requires exchange of this information by something like this Forum here. Anyway, this could give us quite some headache.

Nooneknowswho