For Identity, they invented new rain makers so there would be more dry spaces to work. There was a decent behind the scenes documentary about the process somewhere on the dvd. That's funny you mention Seven because that is the movie that first made me notice rain, because there is a scene where all these drops are hittng the car, but none on the street, so I can't agree Seven did it very well.
That's the way I see it for Identity as well. The rain played a character adding to the atmosphere. I liked Se7en a lot, but you knew what would be in the box at the end. Especially since Brad Pitt's wife had barely any screen time. I knew from the get go she was a kill tool. I found Identity to be less predictible.