I take a cheap $40 US Aiptek digital camera on the more technical rides where I expect to take a spill or two. It's only 1.2 megapixel with no flash or LCD screen so it only does well in bright light. It's only two ounces without the batteries. I wouldn't be heartbroken if I ruined it and for the price, it takes wonderful pics.
I'm usually packing a 3+ lb. (1.5 kg) Minolta Maxxum HTSi film camera on road tours and tamer mountain rides where I'm more comfortable about not hurting myself. After you've learned what you're doing with full manual control, the pics can't be beat. My basic scanner gets me 6-8 megapixels from the basic 4X6 prints.
I can't really take my camera gear with me on the bike even though i'd like to. All the stuff i have is pretty heavy and expensive and i'd hate to fall on it after lugging it up the hills
we do take my girlfriends compact digital (canon IXUS) on all our MTB rides. Its handy for pics of people jumping bikes into lakes, trips to hospital etc