I didn't realize the SD550 was that much larger than the SD400 either, but you're right, it is. The SD400 is only .8 inches, which is over 25% thinner than the SD550. .8 inches is definitely below my threshold for a chubby camera. 
One problem was, when I had my Exilim, EVERYTHING seemed fat. That camera was around 1/3 of an inch thick if I remember correctly.
? Is it a good choice for quality and ruggedness?????
