I beg to differ. I see at least two main arguments here:
Argument 1: Since these publishers are suing IA (premise), I find it justified for myself to boycott them (conclusion)
Argument 2: Well, you were not spending money there anyway (conclusion) if you were downloading your books from IA (premise).
Why did I feel that Argument 2 was unsubstantiated and ad hominem? I asked myself,
how did the person making Argument 2 know that the OP...
(a) ...has used IA National Emergency Library at all? may be they are just unhappy with these publishers bullying an NGO?
(b) ...has used IA NEM to download books from these particular publishers? may be they are buying everything Penguin publishes, but enjoyed using NEM for reading other books from other publishers?
Assuming things about the characters and actions of the person you are discussing with and making your argument about those rather than the topic of discussion, is a sign of a logical fallacy to me.