Just to add a few things, and address some things other said:
First, count me int he club that HATES the idea of a tropical island. Give me a cloudy, grey mountain with a lake nearby, and woods, woods, woods (for instance, I could never visit Pitdog, because I'd go one one of his hikes and refuse to come back). I think part of it is that I grew up int he Northeast. Our house was about 200 yards or so from our own pier on the reservoir. It was maybe a mile to an island in the center, and we'd canoe (later in life I'd swim it, even though we weren't supposed to), and camp out and such. There were other small islands filled with blueberries and such to pick, and we'd eat ourselves sick. Lots of rolling terrain, hardwoods, and the evergreens were mostly blur spruce and such, so you had branches going to the ground you could sleep under in bad weather, unlike the crappy pines down here. In a place like that, I could go a long time, but not outside the time frame of my original answer.
I'm one of those guys that doesn't like a lot of human contact (about as antisocial as they come), but I really like SOME. Going to church once a week is generally enough. Or over someone's house for dinner. But after a couple hours I have to leave.
In a group like the people in this forum, you're going to find the types that can be alone the longest.
One thing I did notice back in my hobo days is that men can go a LOT longer than women without contact. Women get separate, even psycho (more than usual) if left alone for long periods. I'd usually go wilderness squatting (that's what the "respectable" people called it, I called it camping) for anywhere from a couple days to a couple weeks with no real effects. I'd talk to people here and there when I go into town for supplies or work to get money for supplies.
But every so often I'd come across a lone woman. If she hadn't been alone for a long time, she was usually afraid, and worried about being raped or something. But if she'd been alone for a long time, she'd practically latch onto me. Almost as if they'd prefer anything -- even being raped -- to going without attention any longer. Sometimes they just start yammering at mach 3, sometimes, literally grab my arm and beg me to talk to them. Sometimes offer -- services -- just to have some contact. It seemed realyl hard on them.
Some guys were desperate for attention, but they were normally guys that were down on their luck and homeless, not a real hobo. But even they weren't like the women. Most guys, though, that I'd meet ont he road, would just exchange greetings, amybe some info, and then walk on. Sometimes you'd travel together because you were going in the same direction, but would go all day and maybe only say one or two things to each other.