It's not a matter of trust, it is prepartion and my personal experiences with it. When people are cracking open the books they tend to take longer during their turn because they really aren't prepared. I run a game with 7 players and it bothers me when spellcasters have to look up their spells on their turn as well. [slight hijack of an already hijacked thread]Is it really that difficult to lookup your spell while the other 6 players and the DM take their turn?[/end hijack]
So long as you aren't slowing the game, I really don't care. If any of my players decided they wanted to lookup monster stats, for their adversary, in the book, I would be disappointed. Of course, the players might be disappointed when the treasure haul ends up being anemic. There is the Knowledge skill mechanic to obtain monster information legally in the game. I reward those skill choices by making them relevant in the game. If you could lookup summoned creature stats, or wildshape stats, without slowing down the game, then I would be fine because you are prepared. That's all I am asking really. As I said, it isn't trust, it is preparation that I worry about.
My game currently has a Shaman (GR Shaman's Handbook) that has Summoning as a domain and we have a Druid. I play in a game where my PC has a few levels of Druid. We also have a high level Druid and a high level Ranger. I have not seen the Wizard ever use a summoning spell. I can definitely feel the flow of the game shutdown with either group when people are not prepared.