I have a Canon 40D and am thinking about going to the SD990IS for convenience

Will I be disappointed in the quality of pictures? Is there another camera I should consider?

Actually, no. It has the new DIGIC IV processor which does a great deal in improving image quality and face detection. You have to get used to one thing though ... shutter lag. It's a way of life in point and shoot cameras.

Going from a 40D to a SD990 is quite a step downward in overall quality and flexibility of shooting. Comparing a DSLR to a point and shoot is pretty much apples and oranges. You have more features, options, and a lot more camera in the D40. The primary use for a SD990 would be to supplement, not replace your 40D. There are times when carrying a larger DSLR becomes more trouble than it's worth. The SD990 does a good job with what it has to work with (i.e. a small sensor and a limited zoom and a limited amount of flash). It is small and fits in a purse or small bag easily and certainly is more practical to carry when you really don't know if you'll use a camera or not. But I wouldn't retire your 40D. It will easily best any of the small sensor point and shoots of any brand, even with a basic kit lens. Add the fact that you can upgrade to better lenses and add more lighting options with a flash hotshoe and you've got a whole lot more to work with. The SD990 is 14.7MP, but that will produce much less detail than your 40D at 10MP. The sensor on your 40D is so much bigger that the photo/light sensors are spread apart allowing more light sensitivity and detail to be captured. Hope that helps. I use a DSLR much of the time, but carry a SD990 almost 100% of the time.