Yes, it is quite exposed on most of these cameras. The biggest danger is changing lenses in wet conditions (mist, light rain, etc.), where if any of that moisture gets directly to the sensor you're likely to end up with either smears (if you try to wipe it off) or bubbles (if you let it dry) in your photos. So be careful on rainy days, around waterfalls, near the ocean, and other places where there's real water droplets in the air. I'd also point out that pollens can be a problem too, so if you're in the middle of a big pollen proliferation, be careful, too.