Q-Squared is one of my favorite older books. It's been years since I read it, so I can't say how well it would hold up now, but it's just a lot of fun.
I am finishing it up now, and I can tell you it doesn't really hold up. It's written like fan fiction and somewhat poorly at that. It has been disappointing. But the concept is really neat, which is what drew me to it in the first place. As far as I know, it's the only official (though non-canonical) source linking Q and Trelane. (If I'm wrong, let me know so I can go out and get another book!)