Water resistance varies from none at all (most consumer cameras) to acceptable, but not foolproof (professional cameras intended for photojournalism/nature.) The expensive pro models usually have some water sealing gaskets around entry points like buttons and controls, but it's really no guarantee in a solid rain or if they get dunked at all. Also, unless the lens also comes with a seal/gasket/o-ring for the lens mount, that's a weak spot.
For overspray, as long as the drops don't gather and run down inside your camera, it should be safe. Carry a microcloth/small towel to absorb any water that gets on your camera, even from condensation. Keep salt water off, or at least clean off any salty residue carefully as soon as you can.
You can always use plastic bags and rubberbands to seal your camera and lens body if you need to be in the rain/seaspray for any length of time - just take the time to set it up right. I usually cut a small hole for the lens to peek out of, rubber band it, and keep the camera body in the bag with the bag opening towards me to put my hands in - it looks weird, but it works. Just experiment with some kitchen plastic garbage bags and rubber bands.
Otherwise you can buy rain shields that pretty much do the same thing.
The thing is with today's largely electronic cameras, they really don't tolerate moisture nearly as well as old mechanical cameras did - once you fry those circuits, your new dSLR's basically junk.
