Thank you both very much for your replies. Your answers are extremely helpful and it sounds like the newer SDHC USH-I cards are the way to go.
You also both mentioned the sped of the cards. I mostly plan to shoot skills, but maybe some limited video. Also, while most of my shots will probably be single shot, some pix may be shot using continuous. Any additional advice on the speed of the cards would be appreciated. Should I just get the 95MB/s cards to be safe?
And, finally advice on the size of cards would be helpful. Is there any image quality differences among the different sizes?
First, you may have been given some incorrect information.
A SDXC or SDXC UHS-1 card is not compatible and will not work in a T1i. There may be a firmware update, but I haven't located one.
It will work at reduced speed in your S100. Also beware of card write speed ratings. The claimed high write speeds are only for a new or erased cards. Formatting a card in camera does not erase it unless you do a low level format.A low level format takes a long time, and might eatup your battery if done in camera.The only cards compatible with all three cameras are SDHC cards.
Be sure to update firmware in all three bodies.
The size of the card does not make a difference in image quality. SDHC cards are limited to 32GB while SDXC cards are commonly found up to 128GB