I liked the feel and size of the 40D. The speed was perfect for my shooting style as well. be sure to pick each one up to see which one suits you better. i found the jog wheel on the back of the 40D to be a god-send in changing settings on the fly. How the camera feels in your hands is what I deem the #1 consideration. A DSLR may have all the bells and whistles, but if you can't carry it comfortably, then it ends up staying in the bag most of the time, while you pull out the little Canon Powershot instead
I personally found SRAW next to useless. So I wouldn't even take that issue into consideration.
40D is "weathersealed" while the XSi is not. Weather never affected me when I had the original Digital Rebel (300D) so it wasn't a big factor in my decision. Sony, Olympus, and Pentax brag about their weathersealing as well.
My opinion is that if ur going to take ANY SLR to some place that it will get splashed on, dust on, etc...a nice plastic ziplock bag will do wonders. Or you can spend $50 for those "weatherproof" kits for the SLR.
Don't get caught up in the Megapixel hype. it doesn't mean much in the DSLR world. My old 6mp Canon Digital Rebel took fantastic pictures that I can blow up to 11x14 w/o any issues. No P&S can do that. Its a matter of sensor size, not how many MP a camera has.
You'll be hard-pressed to find any other competitor out there with a better 3200 ISO performance than Canon 40D. Nikon's D300 could do better..but its also $700 more. It's in a completely different class than the 40D...hence the huge price gap.
Good luck w/ your purchase