I just got Speedlight 380EX for my Digital Rebel. It seems to be working with the camera's TTL, adjusts itself when focal length changes etc., but whenever I take picture with flash directed at the subject (parallel to the lens) the picture seems way underexposed.When I flip the flash up to bounce it off of the ceiling, the outcome is much better.
The attached examples speak for themselves. Both taken in P program, without any additional adjustments (+/- EV, auto white balance) at ISO 400. I've only decreased the size in Photoshop.