Swarming may account for a few incomplete downloads, but far more are due, I think, to weak connections and network traffic. Uncheck your "remove when inactive" feature for your upload page and you will see. Compared to other programs of its kind, living and deceased, Limewire keeps a connection far less reliably than many others, which means the larger the file, the larger the chance that you will get an incomplete download. That, incidentally, is also why you end up with so many Gnucleus hosts: its I/O is lousy and it never brings you many hosts as an ultrapeer, but it holds on to a connection while other clients flee. Thus they have a tendency to gum up your connections.