The 40D is a very nice camera, even if it's old. It's better built than the newest X0D, being "aluminum-alloy". It's heavier than entry level cameras, and, at least to me, feels great in hand.
It doesn't have the best high ISO capabilities, but I can manage. I'm not doing much low light hand held stuff that requires a fast shutter speed. But you may, so keep that in mind. The 450D handles high ISO better (from what I've seen with my own eyes). The 40D "only" has around 10 mega pixels. Heavy cropping might prove problematic for you, especially if it's noisy.
That said, it's easy to use, the wheels work wonderfully. I don't like the placement of the on/off button, it's just hard to turn on and off!, but that's a minor thing. It's quick, can shoot 6.5 frames per second, I believe. That might come in handy one day when you taking the obligatory droplets shots, or when you're doing sports.
I've been told that CF cards are starting to be "frozen out" on the market, the SD cards are taking over. I'm not sure if that's true, but it's nice to keep in mind.