Do you enjoy playing with a friend in games designed for solo-play? Examples I'm thinking of are Namco's Tales series (or even FFVI/IX's optional use for two controllers, despite being hardly useful).

I think it's loads of fun actually! Even in the Tales games where the AI is great, having a friend play a supporting character in a fight can really allow for more strategious play. I don't get the chance too often, but when someone video game literate is around, I tend to chuck a controller at them for kicks. :D