It is amazing how easy it is to upgrade the memory in the Aero - even for a klutz like me.
I upgraded to 32mb, but would like to go to 64mb at some point. I've had a 256mb CF card in the internal slot previously, though it's in my pocket pc right now.
I've done a little bit of looking around re: smart cards. I don't know much about them, but they seem more for corporate applications, where secure access is an issue. It would be interesting to hear if someone has used a smart card in an Aero.