I was recently ransacking Tony's blog for a picture I could steal. I happened across this entry on Calvin's commentary on Lamentations 3:33. It's especially appropriate to the question of God's wishes or desires (optative expressions). An oldie but goodie.
I also draw your attention to Tony's most recent post, in which he has extracted from his own (and Flynn's ... shhh!) blog the various uses of "optative expressions" that various reformed men have used of God.