Jim, I bought the 40D right away when it first came out so I've worked the shutter out a bit. Compared to my 5d the biggest differences outside of the cropped sensor are:
40d is much faster.
Shutter feels a bit less professional. not the 5d sound!
40d image is more 2d and 5d looks more 3 dimensional.
40d is more prone to fringing or sensor overload.
5d images take pp better, particularly sharpening. If not careful you can easily over sharpen 40d images.
A great camera and an awesome compliment to the 5d. I think the key for you is it's fast and will get you closer than the 5d like your 30d. For your shooting I suspect those 2 things are important. I tend to grab the 5d more often unless I'm shooting action, then the 40d wins. If you are seriously considering at some point when I get time I can take a few sample images with both and post. Just let me know.