So I hate to bump my own post, but I have a few things to add. I still haven't found a thorough review of the T90, but infosync did post a review of it's big brother, the T900. As I feared, they weren't thrilled with the image quality.
So the SD780 and T90 are tiny cameras with HD video and average image quality. Am I hoping for too much if I want an ultracompact with great image quality and HD video? Part of me knows the HD video should be a trivial consideration, but I know I'll use the video mode a lot.