I've used laptops on boats for years, for navigation planning/moving map/GPS receiver upload/download, for processing digital camera photos, for Microsoft Office work, and for Internet (email, weather, googling, website maintenance). Here are my top 10 thoughts on laptops in boats:
1. Watch the power requirement. Laptop cords take 110V power and convert it to about 14 V, depending on the model. Power is not a problem if the boat is plugged into shore power, but is a critical issue when shore power is off. If one powers the laptop from an inverter, then the sequence is this: 12V boat supply, converted to 110V by inverter, then converted to 14V by the laptop's adapter. (amps = watts/volts.) My first IBM Thinkpad running Win98 only required 1.8 amps. New laptops are power-hungry. Without thinking, I bought one that required 9 amps, which was just too much for the boat. I now have a smaller laptop (13" screen) that does everything, including graphics, and draws 4 amps. That's still a fair junk, equivalent to running a water pump constantly, but low enough for most wiring and alternators. It will draw down a battery bank if there is no charging going on, and it makes a small boat inverter work.
2. Keep the laptop small and light as possible: reduces weight, improves storage, and makes carrying easier. Heavier laptops have more inertia, so they are harder to get moving, and harder to stop moving. Things move in boats.
3. Get a laptop toughened for motion, like some of the Toshiba models. Think of the screen hinges and hard drive.
4. Consider screen brightness. Although I never, ever take the laptop on deck, sunlight can stream into a cabin.
5. A swingarm RAM mount to secure the laptop is a good idea, if there is room on the boat. Store in a padded bag. I used to worry about engine vibration, but an ordinary galley place-setting pad seems to take care of that.
6. Backup devices are essential: External hard drive, cards, or thumb drives.
7. For Internet, if the laptop cannot pick up a marina network, I carry the laptop to an Internet cafe. Different wireless devices have different sensitivities (range), but I never worried about that much.
8. Designate a small bag for cords and laptop accessories.
9. "Salt air" corrosion is a real phenomonon, but in my experience if the laptop stays in a dry, ventilated location in the cabin, it does not seem to be a significant problem. Thinking about other electronics I've monitored in various parts of the boats I've had, my guess is that after 5-10 years a laptop opened up after spending a lot of time in a dry boat cabin probably would show more signs of corrosion than one that never goes to sea, but I'm not sure how significant that would be. Depends on whether a tiny critical part is affected, I guess.
10. Consider buying a spare power cord and a spare battery, if going on a long trip. Lose either one and the laptop is dead. Replacements are not always easy to obtain.