I'm also a big proponent of learning how to use tools before moving up to pro equipment. I learned on a Nikon film SLR with black and white film, left it in manual 100% of the time, cheap lens, and i developed my own film.

Only after I mastered that did i get a DSLR.

The SD800 will no doubt let you lean a lot about composition and lighting. But I would recommend getting something with full manual controls in order to truly learn about shutter speed and aperture. If you need any recommendations, let me know!

I very rarely shoot in manual. The cameras really are smarter than 95% of the people out there. What you NEED to learn, is how to creatively control your camera. I shoot in Aperture priority mode. That lets me dictate dept of field. Once you get more experience under your belt, you will begin to recognize scenes that are difficult for your camera to do on auto, and can tweak the settings in, by using manual settings.

Knowing how film works, and all of that, is good... but the most important thing you can do, to get better at photography, is take pictures. Well, take pictures and then critique them afterwords. Figure out what works, what doesn't work. Keep striving for the PERFECT PICTURE. If you ever take the perfect picture, you probably weren't pushing yourself hard enough. I am just an amateur, and like to take pictures for fun, but I also compare my pictures against others, and I know I can hang with so-called professionals. Those people that I choose as virtual mentors, are good. I will always aspire to be in their league... that keeps me growing.