Our new wifi setup kicks ass, and if you're looking for a way to pick up a distant signal, consider what we put together or pieces thereof.
For starters we opted for the Alfa 1000mw USB wifi adapter. Although the older model from it's new type N counterpart, the Alfa 1000mw receives much higher ratings by users. It comes with two antennas, one small, and one HUGE. We installed the huge one. Both antennas come with the purchase of the Alfa.
For a cable, I wanted something long. We found a 32' USB cable. That's longer than the current recommendation for a USB, but ratings and reviews seemed positive so we went for it. Right now we have the antenna sitting inside the cabin in the butterfly hatch (not outside), but we have plenty enough cable left now to put it on the boom of perhaps halfway to a spreader.
We've had this going for a few days now with terrific results. Signals that before were splotchy at best now come in nearly 90%, and that's without raising the transmitter power (available via the software utility). One of the next things we'll be looking to do is permanently mount it, probably on the exterior, and construct some type of weatherproof housing. Another nice thing about this model is that coming in around $40, I'm not going to feel too bad if it lasts a few years or if we decide to upgrade around then.
But the convenience of having a nice high quality broadband connection is terrific. We certainly don't want to spend the money for fancy satellite based options, but if wifi is available and the lack of a decent antenna and adapter is the only thing preventing it from working, that's just sad.
So give it a shot, or at least consider your options for wifi on your boat. Most harbors (including some distant ones in remote areas) now have wifi (even if not always free). A "solid' weatherproof installation might work, but if you want to spend $40-$70 bucks like we did for what's probably going to be several years of good service, make it happen!
From someone who posted a comment below (another Eric) there seems to be a weatherproof container for the Alfa wireless adapter and antenna. I've never used it, but at the cost of $9.99 it seems like it's worth a shot (although not if it destroys a ~$40 adapter). If I get one myself and set it up I'll post some reviews, but in the mean time check it out for yourself and see if you're interested. This would allow the device to be placed on deck, perhaps mounted at the spreader level or other "up there" location. Remember that USB has a maximum distance, so even if you get a 32' USB cable, you'll need that cable to run not only to whatever super structure on deck but also through your cabin interior and safely to where you want to use your computer.