Hi there! Yes, I have a big nose, and I'm left eye dominant (apparently). I'm always hitting the dangblasted ISO button with my nose without realizing it on my XTi. I can't count how many times I'm out in great shooting conditions, I set the ISO correctly, and in the middle of my shooting, I look down and see ISO 1600 or 800 or something.
Rats! It happens to me more often than I'd like.
I have slightly trained myself to keep the camera off my face a bit, but sometimes, when I'm in the hurried frenzy of shooting people or kids that are moving, I'll be shooting like crazy, and then realize that the last volly of shots that I just fired off were in 1600.
It drives me crazy!
I'm so happy to hear that I'm not the only one with this problem.
And if you'd like, you can go see the size of my nose in that thread were we post self portraits of ourselves. 
I don't want to upgrade to the 40D or 50D though. I love the size of the XTi. For me, smaller is better. Just for the sheer fact that I can take it with me more often.
What I really want is the 50D capability in a dSLR the size of the Olympus 420 with an outstanding pancake lens.
Can you imagine how many more places you and your camera could go if it were that compact?
Once again, I live by the motto that the best camera in the world is the one you have with you. 