Dials are blah to me. Size is also blah to me, larger is even a negative because it makes me stand out more as a "pro" to the security in casinos, and weighs more around my neck. if my camera was silver...that would be great! Less chance of being harassed.
I love the dial on my 40D,but you are right on the weight,40d does weigh more,I just know that I prefer the bigger size because I'm use to the 300D.The XT felt too small in my hands.
Mark has the right idea,go to a camera store and try out both of them with your lenses and see which one fits you best.The XS should proove to be an exellant camera with more than enough features that the ordinary snap shooter needs.
Form,how do they harass you?