I'm just after watching sfdebris' latest review
, and he brings up a good point about Q's motivation in Q Who. His idea is that Q was so amused by Picard quoting Hamlet non-ironically in Hide and Q that he sent the ship to meet the Borg knowing that this would lead to Picard's eventual assimilation, and his violent outburst in First Contact would prove to Picard that humans aren't as evolved as he would like to think.
It seems to me that this is very fitting with Q's character, he seems like the sort of bastard that would set up a chain of events that would only reach its pay off a decade later. I think this idea has some merit.