After owning a Canon Digital Rebel XTi for about a year,
I decided to upgrade to a Canon 40D in the Fall of 2007.
You can read a
comparison
of the 40D and XTi here.
One touted feature improvement was "some" weatherproofing,
specifically around the main battery and storage compartments.
Note that the Canon 1-Series cameras use rubber gaskets/seals all around,
including the buttons.
As you can see in the pictures below, foam weatherstripping is used on the Canon 40D. Note also that there are a number of gaps where there is no "compressed" barrier ... although the compartments are groved, which reduces the chance of water/grime getting there. So while this foam weatherstripping will certainly help seal, I'm a bit disappointed as I thought it would be more extensive. Having said that, I've taken my cameras everywhere, (watch a Canon A70 undergo stress/tumble test at Solitude Ski Area) and odds are even with the XTi you'd be OK ... but would have been nice if Canon had upgraded the Canon 40D weatherproofing a bit more.
Canon 40D Storage Compartment
Canon 40D Battery Compartment