I guess the original question was about gear and how others manage it on a bike. . .
I always take a P&S, usually a Canon G11, in the tank bag where I can get at it easily. I don't take pictures while riding because you'll get a better picture if you stop.
Depending on where I'm going, I often will also take a SLR with a couple of lenses. The SLR stays in the tank bag with a small prime (usually a 50mm F1.4) mounted, for landscapes or travel shots. The bulkier lenses are either inside the tail bag or in pouches hung off the tail or seat pack, where I can get them out at a stop.

I take a lot of photos, sometimes from very difficult places (like hanging out of airplanes) and I have two suggestions for carrying gear when you need protection without bulk. . . .first, Aquatech soft wraps are neoprene stretch sleeves designed for lenses and camera body that provide protection against water, dust, and general banging around. They dont take up space when not being used, and are ideal for a lens or camera body tossed in your tank or tail bag . The second suggestion is Think Tank modular lens pouches, which are belt-system lens and camera pouches made for professional photographers, very high quality and easy to hang off a tail or seat bag; they come with rain covers and are pretty much indestructible. The advantage of the pouches is that you can get the lenses out without getting off the bike, or pop the pouch off the bike and put it onto a harness or belt if you set out on foot.