Well, the reading group which was slowly working through Goldblatt's Topoi got about half-way through but has collectively decided that enough is enough! In retrospect I probably suggested the wrong thing to read -- perhaps, after all, the much shorter Lawvere and Rosebrugh's Sets For Mathematics would have been the better bet, as at least we'd have had the satisfaction of getting through it. But Goldblatt's book promised much more meat for logicians to chew on. But most of the group lost its faith that ploughing on was going to deliver more insights. One thing is clear, the book that is going to persuade the generality of logicians or those interested in the foundations of mathematics that it really is important and rewarding to get on top of a substantial amount of category theory has yet to be written. Still, even if I was in the minority, I was left wanting to know more -- so I'm sure I'll return here to the categorial theme in due course.