I vaguely recall reading a long time ago a 50-or-so page paper, either by John Baez or linked from his page (I think the former), which among other things gave a justification for his table of n-categories and a very cute explanation of the realization that really it should start at n=-2. I believe this paper also introduced (to me) the ideas of properties, structure, and stuff. I was just thinking about how I'd love to look back at this, but among the wealth of resources available on Baez's webpage I can't seem to find what I'm looking for. Googling hasn't turned it up either. Does anyone know what paper I'm talking about? And if it doesn't talk about properties, structure, and stuff, can anyone recommend a friendly and polished exposition of these ideas?