We've just received some renderings of the 550D that show some details that people have been asking about (click for larger images in a new window):
Fingertip ISO paddle leverThe larger ISO paddle lever extends the ISO control outward so that it is reachable from the handles. The ISO control is especially important for T2i video shooters as it will be the primary control for adjusting video exposure.
Detail of the locking latches.The locking latches feature both a push button locking release and a mechanical catch that must be overcome, making it virtually impossible to open inadvertently.
Locking latches in open position
Locking latches in open position, detail