Hmm, I saw The Dark Knight preview at my screening. You didn't miss much; it was just the Batman logo slowly eroding with some narration bits in there too. There was no actual movie footage.
As for Alvin and the Chipmunks. To be honest I've always found their high-pitched voices annoying, but I'm glad they kept them for consistency's sake. I think the miniaturizing to actual size works; I think it would look odd to see life-sized chipmunks standing next to Dave.
I dunno, it's hard for me to get excited about something that is not only a typical "Hollywood milks a franchise" film but based on two series I was never particularly fond of (the '80s series especially).